Greetings. I'll cut to the chase and won't explain here in detail what's really going on with this fix or the path that led me to this procedure, but it has now successfully cleared a range of installation problems for iTunes 5.0, 5.01, and QuickTime 7, on two unrelated XP SP2 systems. Feel free to contact me if you want more info, but you may definitely want to give this a try if you're running XP SP2 and have been having iTunes and/or Quicktime 7 install failures (be sure that you are logged in with Administrator privileges).

Important: This procedure should only be attempted if you are running XP with SP2 installed. Also, as is the case whenever making system-related changes, it is always an excellent idea to create a restore point before proceeding:

Given all of the configuration-related variables, this provides a simple mechanism to return to your previous state if you run into problems.

After you've created your restore point:

Click Start

Click Run

Enter in the "Open:" field: "services.msc" [without the quotes ]

Click OK

Scroll down to "Remote Procedure Call (RPC)" [ NOT "Remote Procedure Call (RPC) Locator" ]

Double click on this item

Click the "Log On" tab

If the "Local System Account" selection is already selected, this fix won't help you. If the "Local System Account" selection is NOT selected, SELECT it now. [ make sure that "Allow service to interact with desktop" is not checked ]

Click OK

Close the Services window

Reboot

Try reinstall the 5.0 or 5.01 iTunes + QuickTime package

This may also fix a number of other odd XP SP2 behaviors. Good luck!

--Lauren--