Well, now I know almost everything. But, one more question: is it true, that RPi doesn't play movies (avi or other formats) smothly? I've read that week ago something about that, which made me disapointed
How it is in real?
no not true well.... YMMV
Mpeg4 .264 play fine on standard machines
mpeg2 and VC.1 will play fine when you buy the appropriate licence file
random encoded will have to be decoded in software so make things go chuggy - all depends
but if you have them encoded in a decent format [see h264] and no worries