There is a search button, and just browsing through the forums will answer all those questions...
But what the heck, i'm stuck at work (campus computer lab), no one is here, and I have absolutely NOTHING to do...
Here you go...
1. Depends on how you encode it...(one divx movie is usually 700mb, if you re-encode it to the GP2X's resolution I have most movies to around 250mb and still looking nice, you could make it smaller if you like but I'd say around 4-6 hours on 1Gb is feasible)
2. Build quality is nice, although it admittedly feals a little cheap mainly because it's surprisingly light weight. Overall I am VERY happy with it.
3. Genesis full speed with sound, NES some games are full speed with sound like the first mario bros. but still needs work, snes is slow...too, slow for my liking...C64 is great...PSX is just proof of concept so far in my opinion, but some games (5 at the most and very basic ones at that) do run full speed with no sound...some hardware specific mame emus run pacman and a few others nicely...NeoGeo CD...mmmm...how i love close to full speed Metal Slug with background music (no sound effects yet)...and I don't remember the rest...look in the wiki or on the boards...
Trust me, if you don't mind tinkering with the games and whatnot to get some of them to work (by this i mean getting the right files in the right places and whatnot, kinda tricky for some games), and have most of your videos in xvid/divx format...you will NOT be dissapointed if you buy this...