My computer seems to have a hard time running poser 6. it keeps locking up and crashing and it takes forever to do anything.  what i need to know is what should i upgrade to fix this problem. im also have problems rendering. it keeps saying that there isnt enough memory

my video card is a Radeon 9550 other than that i dont know what determines how well the program will run. please help

edit: Oh and my processer is an intel pentium 4 with 1.8 ghz if that helps