Actually, just do yourself a favor and totally disable UAC. That is one of the silliest things I've seen Microsoft add to Windows. I mean, in theory, it is effective, but it's too much of a nuisance, for this exact reason. God forbid if you want to make any modifications to program files...
I totally disabled UAC and I now have a copy of Vista Ultimate that behaves exactly like XP did; no problems, no hassles.
If you open the Security Center from the Control Panel, you should see UAC options. The first thing you want to do is simply disable UAC; after doing so, you will have to either have to log off, or totally reboot, can't remember which. Once you get yourself rebooted and back to your desktop, you can go back into the Security Center and choose an option in there, something like "change the way UAC notifies me". When you click on that, it will open options, and you want to select the one that says "do not ever notify me (not recommended)". Select that option, and it totally disables UAC and you will never be prompted by that crap again.
Other than that, you might have to manually adjust some of the permissions on files, but typically, that won't be necessary after disabling UAC.
Hope that helps!
Win Vista UAC
UAC isn't there to piss you off. In a rare case, it could fend off a malware or some other kind of attack, so thats why its "recommended". Be cautious. Also, disabling UAC applies to Standard accounts as well. Some things in a standard account will require administrator access, regardless of UAC; key features such as direct tampering with the PC system or Parent control will never work within the Standard user account. Deactivated UAC also won't grant a standard user "normal" program modifying, removing, adding. It can get messed up.
UAC off:
1) unlikely internet originated security breach via bypassing UAC (since its off)
2) loss of security on your computer (a standard user attempting something)