Read http://en.wikipedia.org/wiki/Solid_state_disk and TODAY you can get a 32GB or more all RAM hard disk. Then you can do this.
But as you suspect, any 32 bit OS can't see that RAM above 4GB so you either know your limits or you learn about the limits.
ok what i want is to build a 32 GB ram machine load winxp from HDD then create 30GB ram drive. sector copy c:\ to ramdrive then somehow trick windows into thinking its instaled on the ram drive without shuting down or rebooting. in effect winXP on ram, leave in standby mode and thats it XP on pure ram. should run even faster then the ram by sata controlers like I-ram they have speed limit this hasnt.
if not XP 32bit then 62 bit either way its the same deal i amgine or vista even.