Has anybody had any experience with MythTV? I have an old 2.6ghz AMD CPU that I'm gonna be using. I have either option of Satellite or Freeview. So, can anyone recommend any cards I could use?

I want a dual tuner either way so thats the only requirement. I have XBMC which can use Mythbox, that'll be my frontend.

you could use  a sky card. They are paired to a box, so you will need to obtain the boxkey (easy enough to do)
Maybe a SMARGO USB CAM? really depends on what you want/do

or you could go the dodgy root of cardsharing/paying for an illegal cardshare - google mythtv cccam

I'm looking for a DVB-S2 card. The TBS 6981 is what is recommended about the place and I haven't seen much else that jumps out particularly.

Do you have any experience with setting up your own mythtv box egg?

nope, I use a dreambox