I am not sure which way to go with a upgrade, I will tell you what I have been told the different s are, please put me straight if wrong.

1. 64 bit let,s you use more than 3 gigs of ram.

2. CS4 is set to run 64 bit.

3 64 bit is still lacking in drivers and compatibility problems with older stuff.

4. 32 bit with 3 gig of ram is easily enough to run CS4 and Lightroom.

Cheers