You can actually go two ways with Capture Cards. If you're looking to just transfer Tapes to DVD with little to no editing, you can actually get a card really cheap that'll do the job. It'll record in DVD format in real time and transfer it over to disc. I used a $20 card and it did a servicable job (well, once I found adequate software as what it came with was pitiful).
However, if you want to do some editing, you'll need to capture in AVI or some other easily editable format. There's where you'll have to spend a bit more money. On top of that, you're computer should be up to snuff. Throw some memory at it, make sure you processor is fairly fast (I do fine with a 2.0Ghz P4) and have a dedicated hard drive for capturing.
Right now I'm using a Turtle Beach VideoAdvantage PCI card that also comes with front-inputs that you slip into an 5.25" empty drive slot. It comes with some pretty good software, but unfortunately, doesn't work too well with VirtualDub. It cost around $150 but you can get it sans the front inputs for $100.
I also used the All-in-Wonder PCI, but I wasn't all that crazy about. It worked fine but I don't like having to always update my video card and capture card at the same time (and it has to be the Primary Display Device to work).