The entire interface received a makeover, so it takes a week or so to get used to, but it's still the same Windows underneath (with some nice new features), so there's not much to learn. The major differences:
---------------
*** Great new design, though you can choose to revert to the old Windows95/98/ME look if you want. (To do so, right click the desktop, select properties, click the ''appearance'' tab, and select ''Windows Classic Style'' under ''windows and buttons.''
*** By default, the My Computer, my Documents, and My Network Places icons do not appear on the desktop (only the recycle bin is shown)...they're on the start menu. To bring them back, select the desktop tab, click ''customize desktop,'' and place check marks next to the ones you want. (Then, to chage the start menu, right-click the task bar, select properties, click the "start menu" tab, then select the style you prefer and click "customize.")
*** If you create multiple users, you be greeted with a new login screen. (By default, you'll start with the ''administrator'' account, but it's best to create another one and only use the default for emergencies. (To create new ones, go start->control panel->user accounts->create a new account.)
*** Administrative account have full access to all files, programs, and settings. Limited accounts only have access to their own files, and basic settings, and not all programs may be available for use unless advanced settings are enabled per program.
*** Pressing ctrl+L will allow you to remain logged in to one account, then return to the login screen to log into a second or third. It's a great feature if your spouse or kids need to do something on their accounts, but you don't want to log out and lose what you were doing.
*** Pressing ctrl+alt+delete twice no longer restarts your computer. However, there is an option to restart by pressing the key combination once.
---------------
Aside from that, it's not much different. You'll run in to several other changes and new features, but they're pretty easy to understand and use. Microsoft made this version more ''friendly'' and easier to use/understand than it's previous releases. However, if you ever have a question about anything, feel free to ask in the Windows XP forum. Just think of us as a free version of Best Buy's Geek Squad. 
Hope this helps,
John