The XP CPU has a few diferences fom the old Thunderbird. It has SSE multi media instructions, more 3D Now Instructions, better cache management, it runs cooler that the older Thunderbird CPU and it's optimised for use with DDR ram.
I've read that more software will be written (optimised) to take advantage of the XPs new instruction sets because more people will be buying them instead of P4s (The XP1800 outperformed the P4 2GHz in most tests although it lacks SSE2) <img src="smile.gif" border="0">
I'm going to buy one soon, hope I'm not dissapointed <img src="biggrin.gif" border="0">