Tough call, there is always something new round the next corner.
It is probably worth waiting for the intel macbook to come out, less obvious whether to wait for the OS. Its an easy job to upgrade the OS and you can always do so at a later date when you have a few quid spare.
Apple are always very cadgey about when new products will be released so its your call.
I'm just about to buy an intel Imac, not worried about waiting for Leopard, Tiger is already a very good OS.