No you dont have to use a TV Tuner card, but I agree its one of the best ways. If your VCR has RCA jacks or S-VIDEO you could buy something like dazzle. Then this way you could hook up other devices that use RCA to it as well. I prefer one of the gizmos that has all of that in one nice package such as ATI's All In Wonder series.
I myself had a ATI AIW and it worked great! but I needed more video card power for my games so had to ditch and bought this http://www.adstech.com/products/USBA...?pid=USBAV-704
it require a hefty amount of processing power since it goes through USB so make sure you look at the minimum system requirements.