Back to the topic, the answer is "yes".
You can upgrade it with a P3-850(somewhat abundant) or even a very rare P3-1000 slot 1 Coppermine(FSB=100mhz with full speed L2 cache), and coppermines are way better, almost twice the performance than P3-450 kaimai, which is essencially a PentiumII.
Provided that you must have BIOS upgrade A11 installed at first.
I LOVE XPS T series, IMHO it's the most beautiafully shaped desktop PC ever, and its 440BX-based Intel MOBO is tough and reliable.