I just compiled and ran this on OS X 10.6.6 by creating a byteswap.h and using no more than ./configure and make. (No special options etc.)
Obviously you'll need the OS X developer tools installed but aside from that I did nothing funky.
Just create a file called byteswap.h with the following 4 lines in it in the same directory as everything else.
#include
#define bswap_16(x) OSSwapInt16(x)
#define bswap_32(x) OSSwapInt32(x)
#define bswap_64(x) OSSwapInt64(x)
As far as I can see this is working fine, still testing though but no build probs after that.
Edit : Ah, just saw chromicants patch, that's probably a better way to bundle it into the build

Still, hope this helps someone.
Hi rich_rich. Does your compiled version have the sse2_64 algorithm as an option? If you don't install YASM, the compiler doesn't even try to make the sse2_64 so it works, albeit without sse2_64. If you have YASM however, you get the errors I described earlier in the thread. Still, using one of the other algorithm is a better option for mining than official client.