You can, and here's an older document that shows you how...http://h20000.www2.hp.com/bc/d...ort/...1/c00486161.pdf
The issue may be that the BIOS won't recognize the MT-xx CPU.
Others recommend staying with the ML-xx CPU and undervolting it lower. I haven't did either, but it may be worth a try first...
Athlon 64 3400+ (CG) @ 2.4GHz, Asus K8N-E Deluxe, 2 GB OCZ DDR400, BFG nVidia 6800OC 128MB, Seagate 200GB PATA, Seagate 160GB PATA, Dual Boot XP and x64, Antec 350W Mid-Tower
Athlon 64 3400+ (E3) @ 2.4GHz, Asus K8N-E Deluxe, 2 GB OCZ DDR400, eVGA nVidia 6800 128MB, Seagate 320GB SATA, Vista x64, Antec 350W Mid-Tower