Thanks to all of you who contributed to this thread.
As a result, I've been able to discover that my Dell can, indeed, go from its current 4G memory to 8G, enough to make Win 7/64 worth doing. I've got the memory and the w7 upgrade (from Vista), and I've Acronis to clone my current C-drive onto a new 1TB WD black drive, which will eventually be the new C-drive.
Next, I'll swap the old C for the new one and test, then add the new ram and test again. If all is well at that point, I'll back up everything that isn't already backed up (very little) and try the Win 7 upgrade. The additional memory should help CS4/32 a good bit, I expect.