Uh, yea, called Pagefile. If Both Drives are attached directly to mobo by SATA or EIDE you can place a Page file on both Drives. (If its USB External you could also do this, but then you would have to leave the External on all the time to use its Pagefile)
I myself "alloted" 1024MB to my page file and made it static.
If your talking about the RAM itself. Then no. You cannot manually set what the memory does and what uses it. Whatever is running will be on either just the RAM, the RAM and some pagefile, or just Pagefile. Most programs use mostly RAM and a small small amount of pagefile.
The amount of harddrives, space or partitions you have has nothing to do the RAM and its allocation.