When you insert the Ubuntu CD, and boot to it, instead of just pressing [enter] at the boot screen, type 'server' then press enter - this will prevent it from installing any of the *-desktop packages, and not setting up any unneeded applications.
After following the steps of installation, you will be prompted with a logon screen - enter the username and password you provided during installation, and you are in your brand new Linux system. From here, you can do everything from browse the web, to set up the computer for various networking tasks, to play a range of Linux-based games.
Package management is a critical part of running a Linux system, luckily Ubuntu comes with two distinct and useful tools to aid in your package managing. Aptitude [which, is actually just a UI for apt-get] and apt-get.
A package called "samba" will allow you to set up proper networking between Linux and Windows computers (at least, we hope you've got your networking issues sorted out). Running "sudo apt-get install samba" in your new command line will tell the apt-get application to install the samba package, and set it up with default settings.
Once samba is installed, you'll want to set it up to share certain files/directories, and set them up on your network - samba networking is a massive topic of it's own, and way beyond the scope of this article, however, running "man samba" will give you the samba manual file, which lists off a series of other manuals to look at. Google's always helpful too. :)