Problem is mac is you pretty much buy them from apple as is, you can put more memory in and a larger harddrive etc but as everything is made by apple you can't really source things from other places, Currently they're intel core 2 duo.
Are you looking for a laptop or desktop? You could probably get a 2nd hand one my old emac will still run everything but I prefer my macbook
As for OS you do need Tiger which is the current up to date one, not sure how much stuff runs on Panther I struggled even getting itunes to run as they'd updated it all. Also Leopard is coming out later this year and ooo it looks good hehe that and CS3 and I'm away