One of the main things you need to think about is how
you're going to install your operating system. Most netbooks do not have a CD or DVD drive so whichever OS you choose will need to support being installed from an alternate medium.
Many newer OS's support being installed from a USB flash drive either (almost) out-of-the-box
or after a little light hacking
Many people still prefer Windows XP to Microsoft's latest offerings and there's certainly something to be said for the performance benefits of running XP on hardware that is ten years newer than itself
But there are also caveats to running a 10-year-old operating system. For one, Microsoft will be ending support (updates, patches, etc.) for Windows XP on April 4 of 2014. Sure that's slightly less than three years away but Windows Vista is supported until 2017 and there has been no end-of-life date yet set for Windows 7 (though Windows 7 Enterprise comes with a guarantee of support until at least 2019.)
Another gotcha of running XP is that hardware manufacturers are starting to end support for it. That means that you might have trouble finding the right drivers if you go for Windows XP.
Windows Vista has been much maligned for its shortcomings and heavy resource usage, and mostly with good reason. You can likely expect that running any portable system with Windows Vista (such as a netbook) will mean that you'll end up charging the battery more than you would with a more efficient OS.
Linux-based OS's comes in many, many flavors so it's hard to make generalizations about them with any degree of accuracy. Some flavors are intended for uber-geeks who think in x86 assembly language and have nightmares about the memory management of the PowerPC processor (if you get that joke then you're already a huge Linux geek.) Others are intended for the new Linux user who just wants things to work.
A popular version of Linux among new users is Ubuntu
and its variants
. One interesting and helpful thing about the Ubuntu family (and indeed many Linux flavors) is that they can be run completely from a CD, DVD, or USB flash drive. The practical upshot of that being that not only can you install them from a CD/DVD/flash drive but you can run a fully functional desktop without ever installing anything on your hard drive. This makes for a very nice way of poking and prodding at how an OS looks and feels to you without having to commit yourself to using it. Don't like it? Simply reboot and take out the CD/DVD/flash drive!
Edited by Andrew, 26 May 2011 - 04:03 PM.