I use PowerDVD as well to do the screencaps on my 
site. While it's not perfect, it's the best 
solution I've found thus far. It does the DVD 
decoding in software, but if you have a video 
card with hardware acceleration, it'll pick up on 
that and play it hardware-assisted. You can 
download a 30 day demo that has the screencap 
ability enabled, registration will run you 
$49.50. Check out the site for more info.

-Tony

http://www.gocyberlink.com/english/products/powerd
vd/powerdvd.asp