In your case the only thing you can upgrade are RAM & HDD.
Buy a new one but Wait till company like HP, DELL come with a DX10 Laptop.
My cousin has a Compaq Laptop too (M2000), but the only game it plays without much Effort is Colin McRae 04 & the NFS games (till HP2
). Once i tried playing GTA SA, the HDD & Processor start heating up so quickly.
When you game on your Lappy, Place it on a Table, if possible in a AC room & make sure the Air Vents have more access (no objects placed around the lappy)