I must have been looking at *old* IBM docs that say 32 and 64bit are required for the installer but after experimenting it seems that only the 64bit libs are needed and that's the package that will actually get installed.

http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/index.jsp?topic=%2Fcom.ibm.db2.luw.qb.server.doc%2Fdoc%2Fr0008865.html