With the low cost of ddr2 memory these days, I am looking into some options on how to best use it to improve the performance of ordinary pc activities. For <$100 I can get another 4gb.

One approach is to use some sort of ramdisk software. I have vista-64 bit, and would need to find something that was compatible.
Using it for temporary files would seem a natural. I think the IE temporary files might be good.
I have a good ups, so even some volatile folders might work.

Is there any software out there that can monitor my HDD activity, and tell me where a ramdisk might be most effective?

Any thoughts or experiences on this?