If you want to be able to record 2 shows at once, you either need two different TV tuners, like 2 Hauppauge PVR-150's, or something with dual tuners (like Sellmen said) like the Hauppauge PVR-500, which is a single board but it has two PVR-150 tuners built into it. The advantage of the PVR-500 is that it only needs one cable (coaxial) input, whereas if you get two PVR-150's, you will have to split your cable into 2 feeds, which will weaken the signal.
I would recommed the seperate tuner over the AIW because you can use the seperate tuner for years, while you are more likely to change video cards more often. Also, something like the Hauppauge PVR cards use hardware encoders, which minimizes the CPU power needed to record and encode your TV shows. A typical hardware encoding card will only use something like 5-15% of your total CPU resources, which allows you to do other things at the same time. ATI's AIW cards use software encoders, which can take anywhere from 50-75% (or more) of your total CPU power, which really limits what you can do while recording. If you try to do something CPU intensive while an AIW is recording, you can get lots of dropped frames, which means your recording can end up very choppy.