Well, turning off the "Vista Stuff" will cut the amount of processor/resource use and should then cut the heat generated. Does the cooling fan sound like it's running a lot?
Sudden shutdowns like that are normally caused by excessive heat, so maybe getting the wee beastie's vents cleaned out could be a good idea, you do not wanna know the crud that can get choked up around the intake/exit vents. Get a can of sprayduster and give all the holes a good blast.