Couple of years ago I bought barebones with a micro atx 945GM (ie it supports mobile cpus) stuck 3gb ram in it then just bought a mobile core duo (at the time it was a core duo 1) off ebay.
So many laptops get broke for spares on ebay that I have upgraded the cpu about 3 times in the last 2 years for virtually nothing now running a mobile T7200 core 2 duo which is probably overkill. Any mobile core 2 duo is going to kill an atom.
This route gives you more flexibility, more processing power (also visualization support if you get a mobile chip with it), will run 4gb if you want, easily upgradeable, and probably work out cheaper. Only down side is it it will be slightly more power hungry but only marginally so and certainly way less than what you have at present.