Psh. I run windows apps just fine on my mac. I use VMWare Fusion and have a clean XP install on a virtual machine. If I don't need the entire desktop I can run those windows apps natively within OSX.
Parallels is awesome too, but I've really liked VMWare Fusion.
As far as it goes, you're most going to be concerned with:
1) Screen Size
2) Processing Power (CPU, RAM, Video)
3) Storage Space
4) Battery Life
5) Portability
Netbook -- Isn't going to cut it if you're doing development. Would be fine for checking stats on the road or making changes to ad copy, etc.
What is your normal work environment like? How many apps do you usually run?
I'd say any core2duo should treat you fine. Make sure it has 4gb of ram and hopefully decent battery life.
I get 4 hours off the battery on my Mac, which has suited me fine.
Also.. pfff.. "in-house" apps? I'm sure if you had in house developers building custom applications for you, you wouldn't need to ask us what type of laptop to get.
Just sayin'.