Hi Paul
We may be talking slightly different applications here, but when I used (in 2000) a Hauppauge PCI TV Tuner card that did not have any on-board hardware processing capability, my 1.8G P4 with 512M RAM and a 7200rpm HDD could not keep up with the work load, so I had frame freezing, dropped frames, loss of sync. etc and could not use the PC for anything else whilst watching or recording a TV program.
When I switched to an external
Hauppage WinTV-PVR-USB2 TV Tuner box ($300), with all the processing being done in the box, the problem was fixed, even on my Notebook which is a 3 ½ year old Centrino 1.4G, 512M and 80G HD 5400 rpm.
Similarly, the
Fusion HDTV Dual Tuner PCI card ($199) in my desktop does all the grunt on board in the HW.
All the above are TV Tuner cards for watching TV on your computer and recording to your computer, essentially using it as a personal video recorder.
So, check the USB2 or PCMCIA devices you are interested in and see if they process the video stream using built-in hardware (often referred to as hardware compression) in the device itself. If not, I suspect that your computer will have to wear the processing load which might possibly lead to some the problems I had earlier on, before I purchased the more expensive TV Tuner cards.
Cheers
Dennis