I'm trying to open a .catpart file that my client sent. Is there a program I can download on the Internet compatible with XP Professional?
The file format you are talking about belongs to a company which handles CAD applications and the .catpart is just an object that the software uses in parts assembly. This file format is only accessible to Catia and should be used only to this software because of the compatibility issues. Of course the software is available for all major Windows versions including the one you currently have.