External TV tuner...

Hey all... I've gotten a lot of help from this site in beefing up my home theater rig, and I've got one more head-scratcher that I'd like to ask for a hand with. I'm running my Dell Dimension 8400 (P4 3.2 GHz , 1GB RAM, ATI X1950XT gfx card, Windows MCE 2005 rollup 2) into my Toshiba 32" LCD display, which also has many channels of cable TV, courtesy of Cablevision. I want to add a TV tuner to this setup, since I've got plenty of HD space to use my PC as a DVR. The problem is, I don't have any PCI slots left in my tower, which means I've got to turn to an external tuner. The Hauppaugue WinTV-USB tuners seem to be the best (really only) option out there, but I can't figure out which one to get. I don't want to eliminate my cable box, which seems to be the reason people would get the more expensive boxes. I'm not really sure what the differences are or even how these TV tuners work, I just know that I'd like to build my own DVR rather than pay Cablevision an extra $10/month for it. Thanks in advance for any help!

Nope... no open slots. I've been reading a lot about bottlenecks with the externals and such. I'm not really sure what that means though. Will my PC run slower when recording? With 1GB of RAM, I can see it. Or will the recordings simply be of poorer quality? This is totally uncharted territory for me. Thanks.

I am not sure if this is what you are looking for (Digital Cable Tuner from ATI). Also, I am not exactly sure if mobo needs to be upgraded.

http://ati.amd.com/products/tvwonderdigital/index.html