There are some USB TV cards, the USB 1.1 ones were pretty bad but the USB 2.0 ones should be better (enough bandwidth to work OK).
There have been some PC Card / PCMCIA video capture cards, but be careful some "video in" cards just have a firewire port for a DV cam and what you need is "analog" video in.
about $73 at buy.com :
Hauppage USB dealibob
You might not like the results though, here is what someone said about a similar USB unit from AVerMedia:
"Delay/Performance Problems
The video quality is quite good. But, if you try to input a game console such as Xbox, Gamecube, PS2, to play video games in your vehicle on long trips, forget about it. I ran a Nintendo Game Cube into the composite input and captured to a laptop Pentium III 600Mhz. When you try to play a game and move your character, your character on screen doesn't move until almost a second later. There is a latency, in other words, from when the video hits the avertv usb to when you actually see it on the screen. This makes it a very poor choice for video games, or anything else where you need good audio/video synchronization or "real-time" video. I confirmed this via TV mode by going into a VCR first, then outputting on channel 3. I also tried s-video. They all perform the same way. So not too bad for the price I guess, but not that great, either. I couldn't really find anything else comparable other than the ATI USB, and it's reviews look even worse. I guess I'll just have to break down and buy a flat screen TV with direct video inputs, for the kids in the van on the long trips."