I need to do a custom build, however after my first attempts failed (to boot) I thought I'd see if I could build working firmware at all.  My take on the documentation is that rebuilding RC3 should be about as simple as downloading whiterussian_rc3.tar.bz2, extracting it, and running make twice (saving the defaults as the configuration).  When I do that I get a openwrt-wrt54gs_v4-squashfs.bin that is 1635328 bytes (the distributed version is 1573888 bytes).  Worse yet, the version I build won't boot on the router.  I don't get any build errors.
I'm sure I'm missing some simple step, any help would be appreciated.  Thanks.

I still can't build firmware which matches the rc3 distribution, I'd like to know why?  However, I can build working firmware from the whiterussian branch of the svn repository.  There is one problem with it... /tmp appears to be mapped to ram, but does not show up to 'df'.  Anyone know why that would be?  Thanks.