Bill Northcott has kindly provided a binary package of JAGS for Mac Os X 10.4 (Tiger) and 10.5 (Leopard). You can download it from the JAGS home page. Bill writes:
The attached MacOS disk image package contains JAGS, rjags, the manual and the examples. The code is compiled to run on Tiger 10.4 but I have not had a chance to test that as all my computers have been upgraded. It will certainly work on Leopard for both PowerPC and Intel Macs.
The JAGS binary is three way fat (i386, x86_64, and ppc) which means it runs as 64 bit on a Core2Duo Mac. This works perfectly with R 2.6.1 and rjags which are only 32 bit.