tv tuner card

Sorry, wrong group.

There are many cards that have software for recording video. ATI comes to mind but I have not concerned myself with recording digital broadcasts yet. Perhaps a set top box can tune the digital broadcast and output a format that the soft recorder can use.

The DVICO FusionHDTV stuff works really well
The model without analogue input can be found for $AU150, but the analogue in model is only $50 more, might be worth keeping your options open.
Your 2100 should handle it depending on your graphics card. Analogue out is best done with your graphic card, not the capture card, and it's best to have a card that will do DxVA.
I don't think I'd worry too much about Divx, DVD is the way to go.
Video recording does use a lot of drive space, so that is something to consider.
The other consideration is the signal strength you can get; what looks OK on a TV screen from 10 feet away can look bad on a monitor, and that affects digital reception in a different way, you really do need a good antenna.
Now I've pointed out all the things that can go wrong, I should say digital reception is definately worth it, and being able to do it on your PC gives you much more flexibility.
Standard disclaimer: I don't work for DVICO, nor do I endorse recording of copyright broadcast information. I just know how to do it :)
hth Rob