We were just talking about RAM disks in the Firefox thread, but I guess that's a little more modern than what you're looking at.

I hear XMSDISK, endorsed by Uwe Sieber, is the way to go as far as DOS/Win9x is concerned. And yes, you can even control which part of RAM it uses, apparently.
http://www.uwe-sieber.de/util_e.html

I would recommend RDISK or UIDE by Jack R. Ellis.

RDISK is a RAMdisk, supporting disks up to 2GB. However it is really simple, and once loaded you can only unload it by ctrl-alt-del.
UIDE is my preferred way of filling up otherwise unused RAM, it's a disk cache program that supports up to 4GB of cache, with CD-rom drivers and caching built in (that saves conventional ram!).

Read the manual before trying though, these drivers have a LONG list of options and tweaks.

edit: seems I forgot to add a link: http://johnson.tmfc.net/dos/driver.html

I'm using something called AR Soft RAMDisk. I think it's discontinued and I'm sure there's better options that were given already.
I use it on an old very low power P3 machine which runs MagicJack 24/7 under a stripped down WinXP. I had intended to migrate it to a compactFlash card, but I never completed that transition. In order to reduce disk writes, I use a RAMDisk to hold the minimal sized IE cache, and other temp files and whatever else, I can't remember exactly.
I haven't completely succeeded - the hard disk is set to spin down but it spins back up every few minutes so something is still accessing it. I lost interest in trying to perfect it and have just left it as-is.

shamino wrote:

I haven't completely succeeded - the hard disk is set to spin down but it spins back up every few minutes so something is still accessing it. I lost interest in trying to perfect it and have just left it as-is.

Some programs use quickstarters that read their files every few minutes so that they are constantly kept in memory to speed up their start when they are needed to be used.

Thank you all very much! I'm intending to use a flash card as primary storage device, so shamino's remark is very useful!