The AV500 is good for playing music, there isn't a arrying case out for it yet. The case it comes with is just for storage, it doesn't connect to a belt though. The AV500 will also have a camera attachment soon.
Don't know aout the Gmini, you can goto www.pocketvideo.info for more information.
I was thinking of buying a PVP, but am still not sue which one. the AV500, or the 402cc. my only reason for not buying the AV500 off the bat is the size. I made a cardboard cutout of the AV500, and was like, meh whereas I owned the gmini 400, and really liked the size. I'm real big into music, and like to litsen wherever I go, (school, biking, running, walking, jumping fences, airsofting, blah,blah lots of moving).
so, is the AV500 still okay for moving around in? and is there anything else, like a carrying case where you dont need to put it in your pocket?
thanks for your comments.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic