First off, with PCI x video cards, you usually get MUCH more bang for your buck... I would spend the extra cash for a PCI x board.
I would also reccomend getting the 2.8GHz w/ the HT technology. It improves system performance quite a bit when multitasking, and all HT tech enabled processors come with an 800MHz FSB, while the ones without usually come with 533MHz.
As for the RAM, most (that i have seen) PCI x enabled motherboards now require the use of DDR2 ram, not DDR. DDR2 is a bit more expensive than DDR, and they are not backwards compatible. DDR2 is offered in speeds of 400MHZ, 533MHz, and 667MHz. The faster the RAM you buy, the better, but the mobo might only be compatible with certain speeds.
For a graphics card, if you are looking to spend around $200, I reccomend the ATi radeon x700 pro, for a few hundered more, you can get the x850 pro. If you don't do a lot of gaming, I would go for a lower end ATi card, or buy a motherboard with Integrated Graphics.
Im thinking of upgrading my computer and was wondering what exactly to look for in Mother boards,cpu,graphics card(AGP or PCI X). What are some key things to look for in each of these? Also system bus speed what is it and how do I tell if it goes with the rest of my system (too slow).Also is it worth it to upgrade from a 2.8Ghz cpu without HT to one that has HT? Last but not least when choosing Ram (DDR)how do I know what to pick.