There is a piece of Software for the Palm which simulates an usb-mass-storage device. You can upload and download files on the SD or MMC Card just like with an arbitrary USB Storage Device. This Program runs on your palm and works officially with windows and inofficially with linux. It is 21-Day Try-before-you-buy. Works with my Gentoo and Zire 31.
Just run the program on your palm; You need the "usb-storage" kernel module. Then mount it like an usb-stick. The corresponding entry in my fstab:
/dev/sda1 /mnt/usbstick vfat user,defaults,noauto,sync 0 0
please note the "sync" option; I got problems unmounting without that option.