I have a filter scheme driver with four binaries for 10.4 PPC, 10.4 i386, 10.5 & 10.6 i386 and 10.6 x86_64. I need to put them all into one kext. I don't think I can just lipo them together because of the two different i386 binaries.
How can I get them all into the same kext bundle?
See Apple's SimpleUserClient example: you can use sub-kexts for each OS revision.
Note that you may need to tweak the build settings a bit because later ld versions insert a load command that the earlier kernel linker doesn't understand; see this mailing list message (and the surrounding thread, if you need more context).
(Why on earth was this question marked "non programming related"?)
If you have four separate binaries, you cannot put them into the same kext bundle. You can put up to two binaries into a bundle by putting one bundle into the Plugins directory of the other bundle; the Plugin will match if the inital driver does not. However, if there are no API changes between your kexts, you may be able to use a kext compiled for 10.4 on 10.5 and 10.6, or one compiled for 10.5 on 10.6.