I'd say that PowerDVD is the best to use for what 
you want.  It is a software DVD player, so you 
don't have to have a great video card or decoder 
card.  It DOES let you step through one frame at 
a time on DVDs and VCDs (plays both) though not 
on .MPG files (which it plays as well).  It can 
also take nice screen captures for you--either to 
your clipboard or to a file.

Also, for all you PC users, there is a very easy 
way to take screen captures that not a lot of 
people know about.  Ever wonder what that "Print 
Screen/SysRq" button next to the F1-12 buttons 
does?  It takes a screen capture of your whole 
computer's desktop!  It copies this image to your 
clipboard, so once you press , go 
into MSPaint, Photoshop, etc. and just paste the 
image.  ALso, if you want to take a capture of 
just the top program's window, hold  and 
then press .  It's that easy! ^_^

Oh, also there's a slight problem with this--you 
have to have hardware acceleration turned OFF if 
you're trying to capture a DVD screenshot, 
something from RealPlayer, etc... If you don't, 
you just get a black image where the video was.  
You'll have to look for how to turn hardware 
acceleration off in your program's preferences.

Hope that helps some people!

-Graham