I have 2GB of RAM and two hard drives and I have tried this recently with many different combinations. Here is what I have found, in Windows XP Pro SP2:
(a) with no swap file set, Windows will create its own swap file of around 128MB on drive C: (very bad)
(b) with a swap file set on any drive less than about 40 MB, Windows seems to feel that is insufficient and so it creates its own swap file of around 128MB on drive C: (very bad)
(c) setting a small swap file of fixed size 64 MB on drive D: seems to be enough that Windows does not create its own. Windows also uses a swap file of that size very little, because it is so much smaller than the available physical RAM, so I have not noticed seek noises on drive D: - but I do not think it is possible to get drive D: to spin down.
(d) it is possible to set up a RAM drive which has a swap file on it
if the RAM drive is already configured at boot time: this is because if you change the swap file settings they only become active if you reboot Windows.
The RAM drive software I have tried has mixed results:
Microsoft RAMDRIVE.sys (included in Windows) is limited to 32MB, although see this article to increase it to 64MB:
http://www.tweakxp.com/article37313.aspx
I do not think it can have a swap file on it, but I have not tested extensively due to the low file size limit.
Ramdiskpro is a hack of the quasi-open source Microsoft Ramdrive.sys. I've not tested it yet, but if you are interested see here
http://users.compaqnet.be/cn021945/RAMD ... iskpro.htm
There is a hack out there which can be set to drive B: which I find pleasing as that drive letter is otherwise totally unused. I cannot remember now if it is this hack or another one.
Ramdisk XP from Cenatek cannot easily be used for a swap file, because at boot time it gives you only an unformatted disk (it exactly simulates a physical drive and you have to partition it and format it in order to use it). I do not think that setting it to load an .ISO would help, but again I have not tested thoroughly. There are reportedly some workarounds discussed on the Cenatek forum (see section 3 of the user manual
here) but you have to be a registered user to access the forum.
Ramdisk Plus 8 from Superspeed has system page file support (only in the 'Plus' version: see table of features on this page:
http://www.superspeed.com/desktop/ramdisk.php). It is a premium product at $49.95 but the demo version that I have tried does work well: it loads the ramdrive correctly at boot time, and once you have set it up correctly it has the page file on it from Windows boot without any additional user configuration required. It took me a couple of goes to get this right (the FAQ
here is helpful) and the technical support people were extremely helpful. Although it is a lot of money for one utility, this is so far as I can see the only product which actually does the job - and I think I can justify the expense on the basis it will extend the life of my D: drive by allowing it to be spun down. Recommended.
Edited comments about Ramdisk Plus 8: previously luke-warm comments but I think those were unfair, I am very positive now that I have got it working properly thanks to the product's technical support staff. (Edited a second and third time to add this explanation!)