Do you want to watch broadcast tv (antenna) or cable.
If its broadcast just make sure you buy a digital tuner this is what I have its cheap $22 and I haven't had any problems with it the included software is crap just use windows media center its a great program.
O and if you don't have an antenna you will the need to buy one.
If you want to watch cable things get more complex an a lot more expensive you will need a cable card tuner the I have heard nothing but good things about the ceton infinitv 4 its around $200 i all so found this tuner from hauppauge on Amazon its only about a $100 and has 4 stars on amazon but i haven't seen any reviews for it. the hauppauge has 2 tuners while the ceton has 4 which is over kill for what you want.
The HVR-850 I linked above allows for cable and broadcast. It allows you to do a digital channel as well as an analogue channel scan and even creates a tv guide via windows media center. You can record two different channels at once as well.