That realy depends on which model you get.
In the UK, the 60GB have backwards compatibility, but some of the games get messed up (some sound etc). The 40GB version however, has no backwards compatibility whatsoever.
The 60GB and 20GB in US I think has full backwards compatibility, but I think there is the 80GB version which is also software emulated rather than hardware, and so that has the same problems as the UK version of 60GB.
I think they're phasing out the other SKU's of PS3, so if you don't pick up the right one soon, you may be out of luck. Although on the plus side, I think the PS2's may still be being manufactured (there will be a new PS2 released in Japan, though not sure if it'll come to the UK or US).