I highly recommended WinXP with (graphic Theme turn off)
My old laptop is a Toshiba Protege 7200ct: with only a PII-366mhz and 192mb of RAM
WinXP (tweaked) perform much faster than Win2000-SP4 for me.
However, there is a CATCH, you must turn off the THEME-SERVICE.
Without the Theme, XP looks exactly like the Window2000.
but perform much much faster, especially in boot up.
Aside from Speed, I love the Clear Type feature of XP on the laptop screen.
My old toshiba has a probelm recognizing my older 16-bit PC-card in Window2000-SP4.
but there are no issue when I ran XP-Home.