IBM ThinkPad R40 CPU upgrade

[ThinkPad560X]

I own a IBM ThinkPad R40 not R40e and it has a Intel Pentium Centrino 1.3GHz Processor, Butterfly sticker. And I use it for games now since I got a New ThinkPad. It has 2GB RAM in it with a 120GB Hard Disk Drive, Windows XP Professional.
I'm wanting to upgrade my Processor to a Intel Core Duo or a Intel Core 2 Duo. What one will work inside of it?

[Terrahawk]

The best you'll get into a R40 is a 1.7 GHz Pentium-M Banias (1MB cache). The R40 will not accept anything faster than that, whether it's a Pentium-M Dothan, Core Duo or Core 2 Duo.

[richk]

No dual core CPU will work