Even if you could do this, you'd end up using swap space on your hard drive to make up for it. Your hard drive is many thousands of times slower than your RAM, so the performance of the game would be horrible.
Just about every week, Staples, Best Buy, and every other store that sells computers has some sort of rebate or sale on RAM. Just buy another 128MB or 256MB stick. Your computer will likely seem much faster all around once you do.
I bought zoo tycoon 2 yesterday and installed it on my 650 mhz AMD machine. When i started the game i got an error that i need atleast 256 megz of ram but i've got only 128 mbs. I am not in a position to upgrade. Is there any patch for running it on computers with low memory or can i artificially increase the RAM or atleast show the game that i've got lots of RAM?