I found this on another forum. I know you've got Office XP, but it could help. (The file is apparently hidden on the disc).
"Just a note for anyone else trying to solve this problem for Office 2003 on Windows XP -- I occasionally play around with the services on my machine, disabling those that seem to be sucking up memory for no particular good reason. I was also experiencing the SKU011.CAB problem: I couldn't start Excel, and when it prompted me for the Office installation disc, it wasn't able to find the file, even though I could locate it myself in Windows Explorer. Turns out that one of those services I stopped, called "Office Source Engine", must have been the cause. I just quit out of all my installation/repair dialogs to get back to the desktop, started that service, and was instantly able to open Excel with no problems."