William,
Thief 2 should work fine on Windows XP. There is a patch available at
http://support.eidosinteractive.com/GI/CustomerSupport/patches/PC/thief_meta
lage/thief2107-118.exe.
If you encounter any issues running Thief 2 on your system, please reply
with a copy of your DXDiag text and we will try to work with you to resolve
any issues.
To reply with a dxdiag text:
Click on Start -> Run and type 'dxdiag' in the run box, then click 'Ok'.
When the DirectX Diagnostic Tool window appears you will see tabs across the
top click each tab and run the diagnostic tests on each. Then click the
'Save All Information' button, which will create a text file on your system
where you specify, as in My Documents or Desktop. Open that text file, copy
the contents and paste it to a reply.