I just found this nifty Linux RAM disk mini-howto, created by Van Emery. Might be fun to try sometime.
A RAM disk is a portion of RAM which is being used as if it were a disk drive. RAM disks have fixed sizes, and act like regular disk partitions. Access time is much faster for a RAM disk than for a real, physical disk. However, any data stored on a RAM disk is lost when the system is shut down or powered off. RAM disks can be a great place to store temporary data.Van Emery – Linux Ramdisk mini-HOWTO
The Linux kernel version 2.4 has built-in support for ramdisks.