Yeah, in Win98 there is a RAMDRIVE (or RAMDISK) sys file.
I cant remember which as it was a while ago but if you look for it youll find it.
I am not aware of such a driver for NT/2000 (dunno about ME)
Win98 detects the ramdrive as what it is and provides a drive letter for it.
I am not sure of the size limitation for the device (it is loaded in the config.sys at startup).
I stopped using it because I did not have enough ram to make it worthwile and I think I remember some incompatability with a game or program I used to run (cant remember what now tho as it was a couple of years ago)
I know this is not a complete answer for your question but it is enough for you to solve your query with.
Look for the resources, they are there and with a little thought and experimentation you will work it out.
<b><font color=blue>Cheers</font color=blue></b>