I am booted into Vista at the moment, and checking just now I see that Vista still supports the "Power Users" account of W2K. You can create a user account and make them a member of the Power Users account in Computer Management of Administrative Tools. I suspect W7b still supports this.
In XP, I have 3 user accounts set up: An Administrator account, a Power Users account, and a Users account. I use the Welcome screen to choose which account to log into. For day to day use, I use the Power Users account. It lets me get things done that I cannot do in a regular Users account. For Windows Updates and Installing Software, I use the Administrators account. If I loan my computer to someone else, I log them into the regular Users account. This prevents them from installing software and committing mischief. Only I know the passwords to the Administrators and Power Users accounts.
I have a triple-boot setup with 3 hard drives and 4 OS's. I have XP and Mandriva Linux on the first hard drive, Vista on the second hard drive, and W7b on the third hard drive. The first hard drive is in the main hard drive slot of the machine. The other 2 hard drives I swap out in the Ultrabay 2nd hard drive adapter.
For Vista and W7b, I only use the default Administrators account with UAC turned on. If I want to let someone use my computer for awhile, I boot into XP and log them into the 'restricted' Users account. XP is still my primary OS since Vista is a bit sluggish on my T42 ThinkPad. Happily, W7b is snappier. For the most part, I find myself agreeing with djwayne above regarding UAC.