Hi, I use Superspeeds Ramdisk Plus ver9 on XP 32bit and will happily answer any questions.
My system has 8GB of ram installed (4x2GB). Windows reports the standard 3.25GB. Ramdisk Plus software accesses the entire 8GB.
As I create ramdisks it intelligently uses the ram not accessible by XP first, and only begins to consume the system ram when I make the ramdisk >4.75GB.
Ramdisk Plus has a feature that lets you have the system automatically save and restore the ramdisk contents on system shutdown/boot.
I use my ramdisk for photoshop scratch, IE temp folder, and also I install my frequently used applications to the scratchdisk.
I also run some financial programs that are rate-limited by a process of reading/writing very small files so my 4KB random read/write time is critical to my performance on this app...
Crystal Mark for Ramdisk
For comparison here's the same bench on a relatively new
750GB hitachi drive...great for storage but sucks if you need 4KB random read/write performance.