Recommended / Minimum requirements for full 1080p on htpc

I just bought a samsung 46" 1080p lcd, and working with a ps3 right now for blu-ray. But got me thinking, there must be a way to push full hd through my pc. I've tired multiple times to recode or remux the files to play on ps3 without luck. So I've given up on that.

I've found some trailers from sony, some hd video of shuttle launch and a few .mkv to test.. I've got two pcs; one being macbook 2.2ghz duo2 1GB RAM and a pc with 3.0ghz with 2GB RAM. Neither of them has a "great" video card. But I've recently bought an ati 2600 XT to attempt full hd but was worse off than my gforce 6800GT. lol

So it must be some other requirements my pcs cannot handle these videos. So just what the heck is the minimum and recommended settings to play full 1080p on a pc? Also looking as a htpc, if anybody has bought one of the new shuttle "glamour" pcs with hdmi just for that purpose?

Found this guide helpful http://www.taranfx.com/blog/1080p-minimum-requirements

Even low end hardware can play it