Well to the best of my understanding the 64mb of sdram is shared between storage and actual memory, there's a little bar that lets you allocate more or less to each side, although it's only temporary (I believe).
From what I've seen the 48mb is more for the OS. Since it's larger than the 32mb from the 300mhz people say it's better for future upgrades to the OS.
I think if you want to use a PCMCIA/pc-card in the dell I've seen some places that sell compactflash typeII slot to PCMCIA converters. Some people have posted links on this board but i can't remember where (sorry). Be aware though that it looks weird and sticks out a lot from the top of the device. Maybe someone who has experiencing using the converter/adapter will reply... good luck
you could also wait for those new x-scale processors coming out which is supposed to put all of ours to shame