There are a few options available to you, if you have the means...
You could try an analogue-to-digital converter, like a Hollywood DV-Bridge (
www.dazzle.com), which retails @ £300, or a Formac Studio with a built-in TV tuner @ £350 (
www.formac.com). These are high-end devices that plug into your FireWire port - and have the ability to give you full screen high-resolution captures, as well as offering you the ability to monitor your work on a TV. Although a bit on the expensive side, they are invaluable for giving the best results, and are iMovie and Final Cut Pro compatible.
If you've got a camcorder, or are in the market to buy one, you can use that - most Mini-DV camcorders have an analogue in/out in addition to a DV in/out (i.e. the Sony DCR-PC100 or similar). Yet another expensive option - but worth it if you like to make home videos.
For a low-end result, there are a few USB devices out there (but be warned - they only give you postage-stamped size images, and are intended as a fix for people showing stuff on the web). iRez put out the Capsure - a USB video import device priced at £100. And Eskape Labs (
www.eskapelabs.com) put out the MyTV unit which takes an external video source via USB - and also gives you a TV tuner to boot, so you can watch what's on the box as you surf... That's priced around £120.
P.S. - sorry about using £'s, but I'm sure it will give you a rough idea of pricing.