LR2 came with these 2 versions which one should I have installed. I am using windows xp?? How can you tell which one to use?
From the ReadMe,pdf in the unzipped folder file created when you launch the downloaded Lightroom Program.
64-bit Installation Notes
Mac: Lightroom 2 is a 32-bit application by default. For customers using OS X 10.5 on an Intel-based computer, Lightroom 2.0 can be used as a 64-bit application by selecting ‘Adobe Lightroom 2’ in the Application folder, choosing Get Info(CMD I) and un-checking the ‘Open in 32 Bit Mode’ option.
Windows: The Lightroom installer contains both a 32-bit and 64-bit version of the application. By default, the 64-bit version will be installed only on Windows Vista 64-bit operating systems. All other operating systems will install the 32-bit version by default.
So, for Windows XP, no choice as none is available - you installed the 32 bit version.