Winxp Installation Error

hi guys its me again
My sister gave her old pc to me and I decided to used it on my office network.
Here is the specs AMD Duron 1.1 ghz, 128 mb PC133, 64 mb Nvidia Video Card, 20 Gb HD Seagate and using Win 98.
but I decided to upgrade to winxp. While Im installing the WinXP, an error suddenly apperread it says something like this ..

Error:
Setup had problems registering the following OLE control C:\WINDOWS\System32\initpki.dll DLL: Contact your system administrator, who may provide assistance in diagnosing this problem.
XXX
Error:
The Signature for windows Xp Professional Upgrade is invalid. The error code is 426.
The service has not been started.
XXX
help guys
and any suggestions regarding this ERROR