Just use an easycap usb card. Its what I use. No bigger than a large USB memory stick. Composite and S-Video ports on it too.
The only problem is that the software is iffy on Windows Vista/7, it BSODs if you unplug the device, but if you use some software like Debut Video Capture, or a webcam recording program which allows you to change the input, you should be fine. Also, if you want HD sound, make sure that you use a separate cable for the White and Red plugs, do not use the Easycap plugs as the sound quality is awful. If you use a Red+White to Headphone jack converter, you can get surround sound through it.