My Compaq Evo got broken and because it was unfixable i decided to buy another laptop.

I found a used n800v for 40 bucks.

My old laptop overheated few times a day and made me lose my work.

It was an Athlon XP, while the n800v has a Pentium 4.

So i am wondering which processor is heating more, the Athlon or the Pentium?

Surely, the Athlon. They run quite hot.

If you want to be sure, check for the specific models' TDP (Thermal Design Power).
You can easily do this on Google.
TDP is an indicator of the power that CPU dissipates as heat.
Of course, the more the TDP, the more the CPU does heat.

Pentium 4 on a laptop?
i'd strongly suggest you look for something with a Pentium M (centrino), as they got much better performance/watt (watts directly correspond to heat)

You could take a laptop using a PIII and Intel 830M/MP.They can accept 512 mb DIMMs

The Evo n800v is currently the only laptop i can get since i don't have a lot of money. I will try searching a little bit.