There are 2 RAM slots in mine. I just put in a Crucial 1G stick that I got from ZZF for about $20 less in addition to the original 256M stick. Crucial.com has an online RAM advisory, use it to find your RAM type.
Edit: w00t, post #69 😀
Also, go to dell.com and search for "9300 service manual". The manual shows you how to access the RAM slots and other components.