Be careful using multiple accounts
Windows XP has a unique ability to act like multiple computers on a single machine. This feature was created so that the computer could be used in a business environment allowing each user to have his or her own programs, desktop, passwords and My Documents.
Although setting up multiple user accounts allows for a lot of customization, it has some pretty screwy side effects.
If you have more than one user account set up in Windows XP, many programs allow you to install programs into only one account. This is a nice feature if you only want to install a program into one account, but it can be a real pain when it comes to spyware and viruses.