Serious Laptop Problem

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This seems to have started after I installed Vista Ultimate 64-Bit on it, though I can't see why software would cause this. After being on for 10 mins or so, everything starts lagging (like moving windows around), opening a second program almost kills it. When someone changed their screen name on msn, when my laptop tried to change it, it froze for ages. It running incredibly slow. Also the fans are working like crazy and the air coming out of the laptop is so hot. I have tried holding the laptop in the air for maximum airflow, no help at all. I'm thinking something is overheating, cpu maybe. Anyway here is the spec:

Dell Vostro 1510
Vista Ultimate 64-Bit
2GB RAM DDR2 667MHz
Core 2 Duo 1.8GHz
NVIDIA GeForce 8400M GS 256MB
250GB Sata 5400RPM HDD

Thanks for any help.

EDIT: I might try another OS anyway just incase as its easier than sending it back to Dell. What would be the best choice for that laptop? XP, XP x64, Vista 32, Vista 64 etc?