You need to make sure there are 64-bit drivers for all your hardware before going 64-bit.
If you plan on running windows 7 64bit, you should upgrade your ram to 4gb.... while it would probably run on only 2gb, the experience would be less than satisfactory...
Perhaps I am misinterpreting that statement (forgive me if I am), but it seems to imply that 2Gb would drag down a 64-bit system. That is not true. 64-bit does not
require more RAM - but it will utilize more RAM if available. The operating system will still take advantage of 64-bit even with 2Gb of RAM installed, but it may not be noticeable. Bumping your system to 4Gb will indeed improve performance with 32-bit or 64-bit. But because of overhead and addressing restrictions, a 32-bit system will only see around 3Gb while a 64-bit system can take advantage of the full 4Gb, plus much more.
Either way, your hardware MUST support 64-bit if you wish you go that way. If you can't find 64-bit drivers, you would be better off sticking to 32-bit, or upgrade your hardware first. Note that in "most" cases, 64-bit Vista drivers will work fine with Win7.