I heard about an OS called Puppy Linux. You can find it at puppylinux.com.
It's realy small and when I saw realy small I mean it can fit into a 128 meg flashdrive at least twice. It's based on the linux kernal and most linux apps will work with it. It comes with SeaMonkey, InkPad, Gimp, and a few other programs. Its just about 100% customizable. It it usualy booted from a cd or a flashdrive but you can install it onto yor hardrive if you want. Infact when of my of PCs crashed, i used Puppy Linux to retrieve all my data.
One of Puppy Linux's greatest things is that is uses just the ram.

Its so awsome. You can use it as a developmental os if you dont want to use Windows for writing scripts/applications.

Looks neat =D