For really good quality XVID/DIVX type video, you're looking at approximately 350MB per hour. Most people rip so you can put one movie or two 1hr TV shows on a CDR.
That's about 80-90 hrs for 30GB. It varies a lot though. On the screen of the Archos, you could probably cut the size in half and not notice the quality difference.
With the Archos, they might be talking about the number of hours of video it can record. Don't know if they assume you are using the "best quality" setting on the player.
I think Itunes only works with Ipods, but I haven't tried it, so I can't be sure.
can i put my own dvds onto the computer and then put it on the av 500? also, the ad says the 30gb can hold 130 hrs of video, is that on low quality or is there just one standard quality of video? if the 130 hrs is low quality, how many hrs of video does high quality hold? and can u use itunes to put music onto the av500?