Even if I have a license of Windows XP, when I install my computer I don't use it. There is too much things, I don't need, that consume too much memory of my computer. The default setup of XP isn't very usefull for geek.
The best version I found is "Windows XP SP2 Strip to the Bone Edition". This version can found on the net. It is very small and light weight. It consume very few memory and is really stable.
There's only a little issue: The default keyboard language is english. To correct this you will have to copy the .dll language file (French is kbdfr.dll) and update windows registry:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layouts\0000040C]
"Layout File"="KBDFR.DLL"
"Layout Text"="Français"
"Layout Display Name"="@%SystemRoot%\\system32\\input.dll,-5010"