http://www.esapcsolutions.com/disk-on-chip.htm
However... These buggers are expensive.
16Mb $99.00
32Mb $168.00
48Mb $235.00
64Mb $304.00
etc.
If we get a group of people together, there are volume discounts to be had (for order of 100, 48Mb chips will be under $200/ea).
I don't think it's worth it right now (since you can get a whole new WebPlayer for under $200).
mAx