i would say check the memory...you might have a leak or some of it (depending on how many boards of ram u have) could have gone bad. this is one reason why i dont like useing mac's...these things are hard to check. u might also think of getting adifferent videocard in the future...its a ok card but if u want to do more or serious rendering then it will be slowing you down a LOT in the long run. as for the glitchy software idea...most likely not..there might be a conflict if you have more then one program running at a time but if this problem happens when only one is running then it shouldnt change anything. also the card "can" effect the render. say u use openGl, well that comes from your card not your cpu. and if u installed the extra ram make shure it is in the right way and all the way...part way might cause a conflict that it is trying to deal with. plus it might not match the other ram...ram must have the same clock as each other to work effitiently. as for overheating...it wouldnt just happen..it would happen part way threw the render if at all and most likely not ever. remember even though the mac has a high rating for speed it is still only a 350mhz (in your case) and people with higher mhz put there comps threw mor sh*t then what u are doing and they keep on running. oh well i think that should be enough to get u going...godd luck msg me if u need some more help, i am glad to help if i can -phillycheese81