Just to let you all know it’s possible, I have upgraded my Compaq Presario SR2020NX from the stock AMD Athlon 3500+ to an AMD Athlon 64 x2 4200+. I followed all the links I found on the internet saying that I should upgrade the bios first (see link below) but I am not sure I needed it since I did the upgrade before I even ordered the new processor. The motherboard in this box is the Compaq proprietary ASUS model A8M2N-LA. If you attempt an upgrade, let me know if you try anything faster so I at least know I can go higher if I ever wanted to. I use VMWare and needed more power to handle multiple VMs. This upgrade has helped quite a bit.