a tv card has one or more television tuners, a 'capture card' is typically just one or more sets of inputs, such as RCA and S inputs, which carry a single set of A/V signals and therefore have no need for a tuner. The former accepts antenna, cable, and similar inputs while the latter accepts output from a VCR or other tunable device that delivers only a single channel at a time on its outputs.
i don't recall ever seeing a dual capture card, and analog tuners will almost certainly disappear fairly quickly. ATI's All-In-Wonder and Theater tv cards usually have composite inputs alongside the coax (F) connector, and a number of other vendors' products are popular (e.g. Hauppauge). With only a single composite input per card, you will need two. Finding a card that matches your available slots might be an adventure. If you include (really really) old cards in your search, Miro was very popular.
if you plan on viewing the composite input of such a card in Windows, be aware that Media Center won't do it unless you have an IR Blaster device; you'll need to use the software that comes with the card or 3rd-party capture software. If you already have software that you are required to use for this application, then its docs should enumerate the cards which it supports.