I have both Powerdvd is good for watching dvds at multispeed(read subtitles).. something i do sometimes for masses of anime episodes etc. windvd has better sound, it has the subchannel, so it makes my promedias go boom.
What kind of videocard are you running anyhow? I had a hercules prophet ddr, ran dvd overlay at 1600x1200 just fine, now i'm using a radeon. I run these on a sony g400 monitor. I've been using windvd and powerdvd since powerdvd 1.3. and every revision to current.