Get it Here.
Daemon-tools recently joined forces with Rocketdivision, who in turn used the gooey center of Daemon tools to make "StarPort". Starport allows you to make a RamDisk (among other things) of any size you want, on the fly, without the need to restart.
I looked around awhile ago for RamDisk software, and the general response was that there really wasn't any, asides from a few user unfriendly programs that required a restart to add/modify a RamDisk.
I've been using StarPort for a few days now on Win2k3, and I've made a 600MB ramdisk to play with, it was pretty easy, and I've just been dumping random things on it to play with.
So far I've dumped Half-Life on it just to play it without getting a "loading" screen, and I installed the UT2k4 demo on it to have instant load times.
Either way, I highly recommend anyone with a healthy amount of RAM get this and play with it until they get bored.
HD Tach seems to have difficulty reading hard disks faster than 450MB/s, I assure you it's well over twice as fast as that.