If you can install 64-bit and dont rely on old and obscure drivers, then definately go for it. Remember you can install 32-bit apps on a 64-bit OS, so the only real issue is driver support, for which so far Windows 7 doesnt seem to suffer from... i've not had any driver issues yet.
And obviously your full 4GB memory will be usable under 64-bit... 64-bit has more pro's than con's, though im not yet convinced there's much of a performance difference (if any) apart from it being able to access more than 4GB total system memory.