IIRC with XP they late loaded a lot of things to get the desktop showing faster than 2000. My experience at the time was that while the desktop might have loaded faster it wasn't actually usable for quite awhile after I was looking at it, but that might have had more to do with all the crapware on many XP machines I used at the time.
XP definitely needed more ram than 2000 to function acceptably. I remember 128mb being slow but tolerable on 2000 and absolutely brutal on XP.
>My experience at the time was that while the desktop might have loaded faster it wasn't actually usable for quite awhile after I was looking at it
This, I think the fastboot stuff probably seemed good on development machines used at microsoft, but on the cheap computers loaded with OEM garbage that they were pushing as being capable of running xp, it mostly loaded the desktop and then locked up for several minutes to finish actually booting.
XP definitely needed more ram than 2000 to function acceptably. I remember 128mb being slow but tolerable on 2000 and absolutely brutal on XP.