If you have a 64bit CPU and 4 or more gigs RAM - I see NO reason to have 32bit - for any reason.
Please upgrade with a clean install if you can.
I also like to create a system drive image after I do a clean install, update all drivers, install all patches, etc. Then if windows gets messy or performs bad (too many games, codecs, a virus, etc. installed), just do a image restore and your back in business in a very short time.