BleepingComputer.com: Errors 1721 & 1321

Okay, bear with me as this may take a bit to explain completely. I was trying to install an antivirus program on a friend's computer running Windows Vista Home Edition, and the program required something to unzip it. (It was on a disc he supplied, I didn't ask where he got it from!) After I had downloaded WinZip from download.com and tried to install it, it popped up with Error 1721, "There is a problem with this Windows Installer package. A program required for this install to complete could not be run. Contact your support or package vendor." I then went to the WinZip website, and downloaded a different copy of the program and tried to install it, but I got the same thing. While researching this, I found the Microsoft Installer Cleanup Utility. I figured it would be an easy fix, so I downloaded this. When I went to run it, it popped up with Error 1321, "The Installer has insufficient privileges to modify the file..." blah blah blah. Okay, so I figured it was just a problem with permissions. When I right-clicked on the program, I had it run as an administrator. Error 1321. When I researched this some more, I found the "Take Ownership" registry entries, so I installed this. When I right-clicked on the program again, I didn't get a choice to take ownership of it. So, I backed out one, and took ownership of the entire folder that it is in. Tried to run the utility again, Error 1321. I did some more research, and decided to turn the UAC off. Tried it again, Error 1321. At this point, I read about restarting the computer into Safe Mode, and then clicking on the Administrator account to try to get this utility to run. When the computer restarted in Safe Mode, I didn't have an account login screen. It went right into the desktop. I am not personally that fluent in Vista-ese, so I'm not entirely sure how to tell the computer to show that login screen. I did find some instructions on how to enable the Admin account; something about right clicking on the computer selection in the Start menu, clicking 'manage', and then something about Local Users and Groups, and I don't remember what else. The computer is down the street, and I'm at home typing this on my trusty XP SP3. Anyway, when I tried to enable the Admin account using the 'manage' function, the window that popped up didn't even have a choice for "Local Users and Groups!" Where is that emoticon of a smiley banging its head against a brick wall when I need it!!! Well, I just read that I can enable the Admin account by command prompt, so I guess that's what I'll try tomorrow, if I get a chance. If anybody else has any ideas, please, feel free to throw them my way, because I'm really at a loss here. Hmph, all this just to install a lousy antivirus program. He's lucky I'm not charging him!

Gee, don't everybody rush to help me at once!!! Wow!!!

Okay, here's a little more information. I used the command prompt to enable the admin account, had no problems there, and was able to log in as the Administrator. When I went to run the Microsoft Installer Cleanup Utility, it STILL threw Error 1321 at me and said that I did not have permission to run the program. I also STILL could not get WinZip to install, showing me Error 1721 again. I really don't know what to do here. Do I need to do a repair install of Vista at this point? I could really use some insight here. Thanks in advance.

Okay, its been over a week since I posted my issue, and I have not received ONE reply from anyone, not even a 'Gee, I don't know, but good luck with your issue...' I'm not trying to sound ungrateful here, because I have received a LOT of help from this website in the past. This is why I am surprised that I have not had any luck finding someone to at least try to help me. Oh, well. Thanks anyway. Administrator, please close this post.