dell xps m170 overheat

Hey, so my laptop wasnt used really for about a year. Before that I used to it mainly game, played wow and oblivion sometimes, and I never had any problems. My screen went out and I never replaced it for a long time, so just about a month ago I got it going again. Anyways I have played certain games on it and pretty much anything I play will end up shutting down my computer after a couple minutes saying it became warmer then expected. I did a search and saw about cleaning out the dust, Ive got an air compressor so im going to blow it out today. Also the only change I made to it was switching to a slower hard drive, from 7200 to 5400, so that should be even better on heat (hitachi travelstar) and from 1 gig of ram to 2. Its also got a 2ghz pentium m and a 7800gtx.

Is there anyway adding 1 more gig of ram could cause this? I highly doubt this... but still wondering. Also was wondering what kinda temps I should be seeing on certain components?

Thanks

Ok so I did clean the heat sinks and fans with an air compressor, there was so much dust in there, i use to clean it pretty often but havent for quite a while. Also i have it propped up a little in the back now as well. What a difference cleaning that has made so far, fans havent gone to full speed yet, ill see how it is after longer sessions.