Your motherboard's socket is actually known as "
socket P" and you can replace the processor. Your laptop's chipset is
GL40.
Your chipset will only natively accept 800MHz processors on socket P, to rephrase that: your laptop will accept
any socket P processor with 800MHz FSB. By that you are limited to certain Core 2 Duo processors and cannot accept Core 2 Quads (C2Q's unfortunately start at 1066MHz FSB). If you install a 1066MHz CPU, your laptop will not boot.
The T9300 is almost identical to the T9500, the only difference being the T9300 is clocked at a mere 100MHz lower; hence the T9300 is the best choice for a balance between performance and price. You should be able to accept all the following Core 2 Duo processors (higher you are on the list, the better the CPU is):
Intel Core 2 Duo
T9500
T9300
T8300
T8100
T7800
T7700
T7500
T7300
T7250
T7100
T6970
T6900
T6670
T6600
T6570
T6500
T6400
T5900
T5870
T5800
T5670
T5470
T5270
Your motherboard/chipset will also support Pentium and Celeron Dual-Core in addition to the single-core Celeron processors, however I would recommend a Core 2 Duo CPU. If you're also willing to experiment with your laptop, you maybe able to accept some 1066MHz CPU's if you physically modify your socket; which is a basic procedure allowing you to accept the otherwise non-supported 1066MHz CPU's.
This is known as the BSEL Mod, and you can read more about it here. The BSEL mod will allow you to run 1066MHz CPU downclocked at 800MHz, hence you may gain better performance sticking to 800MHz CPU's anyhow.
I'd purchase the T9300 processor, try searching on eBay. The T9300 is a Core 2 Duo CPU which is compatible with your laptop.
All the best.