If I sorted out the motherboard options correctly you have the HP Leonite-GL8E motherboard. You might want to run Speccy and see if you can confirm that. Motherboard specifications
Motherboard manufacturer's name: ASUS P5LP-LE 945G chipset.
HP/Compaq name: Leonite-GL8E
FSB support for 800Mhz and 1066Mhz
CPU support: Core 2 Duo E6x00 and Core 2 Duo E4x00
No support for Quad core CPUs or Wolfdale dual core CPUs or E6850.
There really isn't a much of an upgrade option for that motherboard. E6700 OEM $172.50
or E4700 Core 2 Duo 2.60 GHz $145
IMO it's not a big enough bump up in performance going from 2.13Ghz to 2.6Ghz & 2.66Ghz to be worth that $145 & $172.50.