sounds like a hard disk problem.
Can you boot from the Windows XP CD at all? If yes, take a look here:
http://support.microsoft.com/kb/307654
Read the sections headed:
How to use the Recovery Console,
How to use the Recovery Console command prompt and
Command actions
Particular attention to:
Chkdsk
If you can't boot from the CD, then try this:
Do you have access to another PC? If so, then you can slave your hard disk and run a scan on it.
Looking at the Fujitsu Siemens SCALEO 600, they come with both IDE and SATA compatibility, so depending on the hardware type, here's what you do:
Find someone with a spare PC:
Remove the hard disk from your PC
Install into the spare PC's secondary IDE channel - usually what the CD drive is plugged in to. OR Install into the spare PC's second SATA channel
Boot the spare PC, it will (hopefully) find your hard disk and install a generic driver.
Once that's finished, open up Windows Explorer, right click the newly found hard disk
Right Click>Properties>Tools
Choose Check Now under Error-Checking
Tick the 2 boxes and click start
You may be prompted to restart the PC, if so - do so.
That will run a surface scan of your hard disk and tell you if it has any errors.