I just wanted to add my $0.02 here too.
Some suggestions to make browsing as private as possible. Some of this has been talked about above and suggested, but I wanted to be as through as possible and all in one place.
1) Use a totally out of character username for the forum. Something someone who knows you would never guess.
2) Use a completely dedicated, web based email address. And only access it through private browsing (see below). Google, Yahoo and Hotmail are some of the more common ones. Also make this something no one else would guess.
3) Use InPrivate Browsing. Just about all the major internet browsers have some form of this now. Internet Explorer 8 has this listed under "safety" on the tool bar. When used, this stops the computer from logging any info to your HDD (hard drive) including cookies, and history.
4)Password protect your computer. Most of the newer OS' out there have a very simple interface for this. Even a search on the web or in the help topics will be enough for most people to get this up and running. Generally speaking, the bigger the password the better... .
For a lot of people the above steps could be enough. If you're still concerned, some of the following may help.
5) Make sure you have a reputable Anti-virus/Anti-malware software installed. These should find most tracking cookies and malicious software. Including some software based keyloggers.
6)For windows users, check your Task Manager and Processes Tab for programs running that you are not familure with. If you're not sure about something, right click on the [Insert name here].exe and go to properties. If you're still not sure, Google is golden . Do a quick search just to see what the program is. Do NOT just randomly start shutting down processes though! That could cause your computer to become unstable and act "wonky" at best and crash at worst.
7) Hardware based Keyloggers are VERY noticable. They plug into your computer and your keyboard plugs into them. Old style PS2 keyboards (round plug with pins inside) may be a problem since most computers only have that socket at the back, but the easiest way to deal with USB keyboards is to either plug them into the front of your computer or use a simple USB hub that sits on you're desktop in plain view.
8) If you feel the need to bookmark something, only do so on an encrypted drive. Windows 7 Professional and Ultimate editions come with free encryption software called "Bit Locker". In my case I have an OLD 10 GB HDD that is encrypted, this needent be anything fancy and picking up an old HDD off Kijiji or Craigslist is normally pretty cheap. You can configure the software so the drive is always encrypted (locked) when you start your computer. When you shut down after unlocking the drive the next time the computer is turned on it will be locked again. There is also a "mobile" version of this software, it works for USB drives and memory cards/sticks. Word of warning though! When you first encrypt the drive, you are given a "key". If you forget your password this is the only way to recover the information on that drive. If you save this key to your computer it's the digital equivelant of leaving you're extra house key under the door mat... .not much point

. My solution to this is I haven't saved anything vitally important to the encrypted drive. If I loose the data, it's not the end of the world. Also for this reason, I don't recommend encrypting your whole HDD. There is also freeware encryption software on the net, I just can't speak to it's effectiveness.
For people with a Home Network.
9) Routers log EVERYTHING that goes through them to some extent. The Router Log contains Ip addresses showing what, where and when you've been somewhere on the net, even if you're browsing privately. Each model of router is going to be a little different, so some research into your particular model is going to be needed if this is a concern for you. Most people don't even know about this and even fewer yet know what they are looking at if they do stumble across it. The easiest way to protect yourself here is to make sure you have a strong, random password for your router's interface page. (Again, it's going to vary from model to model, but try typing in 192.168.1.1 into you're browsers address line to see your router's page. All the routers I've had used this internal address by default. Default username and Password on my last 2 different routers was "admin" and "admin" respectivly)
10) Make sure you're not sharing anything that could be considered "sensative" on your home network. Easiest way to ensure this is turn off network shareing for you're files/HDDs.
One extreme step... .
11) If after all that you're still concerned. There are free OS' (Operating Systems) out there. Most of them are Linux based and can actually be run off of a CD or DVD (called a LiveCD). I've only downloaded a few to try out but there are a WIDE variety of them. For the most part how this works is you download the OS from the website and burn the ISO file (Disk image) to a CD or DVD. When you want to use the disk, simply put it in your CD/DVD drive, start up and boot from that drive (there should be an option for this in your BIOS under "boot priority" or something along those lines). The OS will ask you if you want to "try" or "install", choose Try. The advantage to this option is NO information what-so-ever will be on your regular OS and NOTHING of your session with the LiveCD can be tracked (except for on the router)... .but, it is a little bit of a pain because you'll have to configure the whole system and your internet connection EVERY time you use it. For a list of possible OS' google "FreeByte Operating systems", Freebyte is a site that has links to MANY downloads for a WIDE variety of programs.
Due to the wide variety of software and hardware out there, I can't possible be able to give details for how to go about all this... .I'm just posting this as a starting point, something for you to look into if security is a concern.
And now, ALL that said... .there's still no way to say 100% "I'm secure!"... .there is ALWAYS a risk and there's only so much you can do. This is the internet, once something is put out there, it's there for good.