It is only the Gamaing that will alter a decision here, imho.
As that's the only thing where a graphics chipset has to be thought about, the Dell Inspiron 8600 would be a general gaming choice (for example), you get the ATI 9600 mobile or the GeForceFX 5200Go standard. rather than the build in Intel type.
I have a 2 year old PIII-m 1GHz and web browsing, wors, programming (.NET 2003) are all handled very well.
As you are programming I would recommend getting a higher resolution screen, I have a 1400x1050, the 15" + er will be 1600x1200 or whatever the wide screen equivalent are.
The text is smaller, but as your not far away from the screen and LCD have very sharp text I can tell you the extra 'space' is a god send when programming.
You can always switch to large font etc as well
The Pentium-M (Centrino brand) will do everything the P4-m will do, for what you want with a lot better battery requirments. Just buy with Wi-Fi (if it Centrino branded you have it anyway
) Get a second battery and use two at one if it's capable of it.
Make sure you get at least 512MB of ram. That will not just make it nicer to use, but should extend your battery life as the Harddrive doesn't get used so much.