That would be the T7800 Core 2 - 2.6 GHz.  It isn't worth the trouble unless you can find one basically free of charge - the performance boost is all but imperceptible under most uses.

the t9900 maybe the qx9300?

No - those require a bus speed (1066 MHz) your system doesn't support.

hi, In the spec's It has this: External bus frequency (front side bus) 800 MHz (Intel Core 2 Duo processor) 1066 MHz (Intel 45 nm Core 2 Duo processor

No  -- the chipset in the M1730 is 800 MHz or lower - no 1066.

Hi ,Will they work in a xps m1730 ? Thanks mark

Not sure where that came from but the M1730 uses the Intel 965PM chipset -- this predates arrival of the 1066 MHz bus (Montevina, GM45  and successor chipsets).

The 965PM doesn't support CPUs with FSB above 800 MHz.

Hi, It came from the Dell™ XPS™ M1730 Owner’s Manual as per: Specifications NOTE: Offerings may vary by region. For more information regarding the configuration of your computer, click Start→ Help and Support and select the option to view information about your computer. Processor Processor type Intel® Core™ 2 Duo processor Intel® 45 nm Core™ 2 Duo processor L1 cache 64 KB L2 cache 2 MB or 4 MB (Intel Core 2 Duo processor) 6 MB (Intel 45 nm Core 2 Duo processor) External bus frequency (front side bus) 800 MHz (Intel Core 2 Duo processor) 1066 MHz (Intel 45 nm Core 2 Duo processor) System Information System chip set Mobile Intel 965PM Data bus width 64 bits DRAM bus width dual channel bus Processor address bus width 32 bits Flash EPROM 2 MB PCI bus (PCI-Express used for video controllers)