online updates of flash card images

Does anyone have any suggestions for a method of updating flash card
images over a network? I'm using a non-standard distribution of linux,
which uses the syslinux boot. My code image will be about 2 Gig, and I
only have 512M of RAM, so that eliminates running things out of RAM. I
can use a larger CF card, so I'd be able to store a second image as
it's recieved. Any ideas? Thanks.
.