Default Really Need SOme Help With P6500

hi guys i really need some help, i have just taken deliver of 3 new P6500 running WM6.1, for my work i must use a pice of software that communicates with the head office with GPRS, unfortunatly it only works on WM5, currently they have not strared to work on a version that works on WM6.

i need to install a WM5 rom on this PDA, is it possible ? if so how would i do it? i am very IT literate but dont know the ins and outs of the HTC ststem for roms

i would really appreciate any help given