Yes, adaptec videoh! media center usb 2.0 edition has coax input in addition to component and s-video.
I just got it and it seems to be fairly good. I haven't had time to play around with it much though since i just got it set up.
You might want to think about investing in the Snapstream PVS3 software too instead of using the one that came with the tuner (actually if you decide to buy some other tuner you might still want to get this software anyways, as long as your tuner is compatible). I played around with the settings and it looks like you can get the live tv picture quality to be a little better than the tuner software. Also you get lots of other cool features which I won't go into here. PVS3 can also be set up with an IR blaster for changing channels on cable boxes from your computer (This is almost a must have if you use cable boxes to descramble your cable signal). Its actually the main reason I got the PVS3 software. You don't want to have to change channels manually using the cable box remote, especially if you want to automatically record shows on different channels (one after the other of course, not simultaneous, thats impossible). They even sell it on their website (even though its on backorder still ugh... and they won't offer tech support for it because it doesn't work on a few brands of boxes). Oh, one more thing, if you do get PVS3 for the adaptec tuner, make sure you download the patch to upgrade it to version 3.2. I initally could not get the sound to work on PVS3 but after installing the patch everthing ran perfectly.
Oh yeah, I'm running all of this on an Inspiron 8600, 1.7 ghz, 2 gig ram, geforce fx go 5650.