I would be guessing here, not having ever installed extra libs for gimp but you would probably have to match 32bit and 64bit together so 64 bit gimp would probably need 64bit libs etc. Otherwise don't really know.
If you need to know whether the gimp is running in 32 or 64 bit then you can run up the process explorer and it might tell you. Certainly the process explorer from sys internals (.com) will tell you.
If your on a 64 bit PC and you need to run in 32bit environment then you can run up IE in 32 bit. There's shortcuts for each type. From there you can launch installers and stuff and it should install into the 32 bit area or 64 depending on which IE you ran.
I am sure that somebody out there has done it correctly - prob just a case of searching for the chappie who managed it. I shouldn't think you would have to build it.