Looks like if your board is that PCChips M810, you have 2 DIMM slots.
From newegg.com, you could get a pqi 512MB PC133 stick for $53, add $5 for shipping, and get $5 back from a mail in rebate, if you wish.
http://www.newegg.com/Product/Product.asp?Item=N82E16820141515
or for a couple...