If still unsolved, here are some options (& reasons.)
(Long version with explanation & alternatives for archive's sake
As previous poster stated, running as adminstrator gives you the priveleges to do it. You may have a "limited" (versus Administrator-level) account, which means your permissions/what you can/can't do are restricted.
When jithin said to "run as administrator," he may have meant the control panel.
This is tricky, as it's part of Windows Explorer.
In XP, search for "Control Panel." When it comes up in your results, right-click, then choose "Run as...," and, in the dialogue box, choose option 2: Run as Administrator.
You'll need his password (or whatever Admin-level password was used when the computer was first setup.)
To use his password, the Admin password (same "level," just not the one used when setting-up,) do the same thing. Find the Control Panel, right-click, choose "Run As...," "Administrator," but this time do 1 thing different: Where it says "Administrator" in the drop-down box in option 2, choose his logon name, then he can use his password!
When it comes to uninstalling the program, richc46 pointed out an awesome approach: an Advanced Uninstall.
Programs like RevoUninstaller are awesome because they not only remove your program (or whatever you DON'T want,) but also:
- take leftover files along with
- take registry keys with... (so you don't get errors if you put it back on, like Trend Micro Internet Security, which has to be TOTALLY DELETED to reinstall successfully.)
An alternative (which has a great 15-day trial that allows you access to everything is Yamicsoft's XP/Vista/7 Manager. Get it from either download.com for free or Yamicsoft.com. They support x64 environments & to use their "Smart Uninstaller," go to "Cleaner" (left-hand side/column,) and find Smart Uninstaller. A recommended adjunct is to click the blue link at the top of that window called "Find Invalid Programs and Files Folders."
NOTE: Don't delete all results in that; only check (and delete) leftover folders for stuff you're SURE you removed. If it says something like "Intel," "Adobe," "Apple," etc., and simply returns an error of "Missing .exe file" or "null," then leave them alone. This could affect your system drivers.