32 bit or 64 bit?

Nope - Won't be faster. It'll be about the same.

Also, Vista 64's Superfetch will find use for 2 GB of RAM quickly. 4 GBs would run much faster allowing for more frequently used data to be stored and then quickly accessed in system RAM. Vista 64 and 2 GB RAM, Nah.

With only 2 gb it's not worth the hassle of reinstalling, first a clean install of Vista 64 then all the programs and updates, not to mention chasing up 64 bit drivers for all your hardware.