Netbooks, ahh netbooks...
Ok first I'm assuming you're not going for an ION netbook (superior IMO, but not out for another month or so in most places) so that leaves us with an Atom 270/280 and a GMA950. (Not counting the n10j which has the price that you may as well get a full note book)
You have a couple of options, some netbooks come with solid state drives, and others standard 2.5 laptop drives (usually 160gb). IMO get the 2.5 inch models, you can always upgrade to a 2.5 inch solid state drive if you want.
Keep an eye on the battery size, I wouldn't go for anything other less than a 6-cell.
The biggest headache that people seem to run into with netbooks is the screen resolution... that x600 is a PIA for most people (Some games even if they'll run with the Atom/GMA won't run because of the resolution). You may want to look at the HP netbooks, their 10inch line has a $30 USD upgrade to a 1366x768 screen. That right there will open a lot of gaming doors, not to mention full 720p resolution (with a bit to spare).
With that in mind one of the first things you'll want to do with a netbook is upgrade the ram to 2GB (cheap and well worth it). Also I'm assuming you went with a 2.5inch drive and not a solid state one, or you'll end up hurting for space.
Also check out GMABooster, and play with OCing the Atom (The 270's OC a LOT better than the 280's, due to locked multipliers). Turn off Search Indexing, Disable NTSP last access, turn off the GUI eye candy (System Properties (right click on my computer), advanced, performance, set for best performance). Clean up the startup apps, and defrag regularly.
Finally if you run into a game requiring T&L yet not needing high power, check out "3D ANALYZE" it's a Hardware T&L emulator that can be used on Netbooks to trick games into running.
Finally have fun with it. :) Get some good old games (gee, I can't think of where to buy any of those) and some newer ones. and also look into a good case/sling bag and a small external mouse if you like.