^2GB MAX - http://www.crucial.com/store/listparts.aspx?model=Presario%20SR2002X
2X1GB - 2GB is fine of Windows XP/Vista/7 32-bit OS. And no it is NOT possible to add additional slots or go past 2GB with your MOBO it is a H/W limit. Alternative, is to replace MOB which on a Compaq Presario is nearly impossible; it would be easier to get new case and probably build a completely new PC.
Good Luck and I hope this answered your questions!