Windows XP Home, Setup failure, Error message

  I have a lot of crashes and application freezes, which occasionally free
themselves, but more often not. I decided to renew my Setup, hoping to find a
Repair facility on my legal Windows XP / SP2 Upgrade (from Windows 98) CD.
Each time I get into "copying installation files" the setup stops and I get
this message, for which I cannot find an explanation, or a cure, anywhere!
Quote -
"Windows Setup"
Setup was unable to read from or write to Drive C. If a virus scanner is
running, disable it and restart Setup."
End quote.
During this process I don't have any virus scanner or other programs
running. Virus-wise, my computer is "clean".
Can anyone help me get around this, please, and how do I activate a "Repair"?
Thanks.

--
Robin Oram
Portugal