Rroberto18 asked the Answer Line forum about administrator, regular, and guest user accounts.
You definitely need at least one administrator account. Windows won't let you have less than that--and with good reason. Without an administrator account, you can't install software or change Windows' configuration
Conventional wisdom states that you should use your administrator account strictly for administrator-level tasks, and use a standard user account (called a limited account in XP) for your day-to-day work. I have to admit that I find working like this highly annoying and I do everything in my administrator account.
If other people are sharing your computer, you should probably give them standard accounts. Two administrators only makes sense if both people are knowledgeable about Windows and frequently discuss how they want the PC set up.
Your computer has a Guest account, which you can turn off if you don't want it. The Guest account is worth keeping on if you want to give friends or houseguests occasional but limited access to your computer. But if you don't intend to share your computer, turning it off will be more secure.