Hard question to answer. There are some advantages (de o hardware archtechture changes), but until you are able to run a 64-bit OS and 64-bit applications (which won’t happen until enough 64-bit systems are on desktops), you won’t get the *full* advantage.
Even if you’re able to just step up to a 64-bit OS, there are some reasonably big wins there, as the 64-bit systems can typcially move memory and do I/O faster.
I assume we’re talking about an AMD64 system? Otherwise the answers are much different.
-Scott