I was doing some checking and I found a few websites that have really good tutorials on how to switch from Windows to Ubuntu:

https://help.ubuntu.com/community/SwitchingToUbuntu/FromWindows

http://monkeyblog.org/ubuntu/installing/

http://www.buildyourown.org.uk/pc-installing/ubuntu/

One thing I should mention from personal experience is that the Migration Assistance really sucks sometimes. When I first installed Ubuntu it was quick and painless, but upon a re-install on a dual boot machine the installer would infinitely stick on the account migration. If this happens to you, you’ll need to reboot from the CD, log into the terminal, then run the installer without the Migration Assistant:

user@localhost:~$ ubiquity –migration-assistant