I know at least I had some confusion early on with what types of memory the 770 would take, Cliff Notes version is MMC Mobile and RS-MMC work great. You can get MMC Mobile 1 Gig sticks from Meritline.com for $31 now, I have one and I also bought 2x 512 sticks when they went on sale for $11 (try to get a couple gigs at one time as $11 for a stick plus $6.95 s&h peeves at least me off). RS-MMC seems to run quite a bit higher and doesnt seem to be any better than Dual Voltage MMC Mobile

Ive got some audio books and MP3s on my sticks but mainly I use them for video.