I use an RGB capture card with some custom software (Which I traded a neo setup for, happily enough) rigged to a foot pedal* so I can snap pics without moving my hands from the stick.
Consumer-grade capture cards only snap pics at 30Hz, so you'll get two frames blurrily superimposed most of the time. Unfortunately higher end cards that do a real 60Hz are many hundreds of dollars. The best screengrab I've seen is on a $1200 card - it looks like an emulator screendump.
Lawrence.
*it's not really a foot pedal so much as a neo stick on the floor with all the buttons mapped to 'screendump'. =)
[edit: Here's a sample]
<img src="http://nfg.2y.net/ebay/neo_kof1.png" alt=" - " />
<small>[ August 12, 2003, 12:22 AM: Message edited by: NEOGEOman ]</small>