Also depends on the use.
As MPower said, you're prolly not gonna get a good result if you're looking to do a full-size print poster from a straight out video or screen capture. But for web use, like Oleg's masterpieces, you're fine.
Here's the other trick -- copyright.
If it's just for your personal use, or for this little community, you probably fall under "fair use." However, if you're going to post this poster up for the outside world, and ESPECIALLY if you're looking to make money out of it somehow (even ads on your website, for example) you're asking for trouble. Now Paramount (or whoever) isn't likely to waste effort tracking you down I'd say -- but then again since this board started sending complaints to HK and Glock about VPC's website, you never know who might try to rat you out from the other side.
Can you maybe tell us a little more about what you want to do? Like -- what format do you have the movie in, what equipment/software do you have for designing the poster, and what's your intended final output?
Then we could give you more specific advice...
[This message has been edited by Kaylee (edited August 04, 2000).]