Ok so you have a couple choices. You use standalone(No data plan) gps with your current stock rom or go to a custom rom. Which do you want instuctions for?
Assuming you want custom rom.
Here is tutorial for unlocking phone for custom rom
http://forum.ppcgeeks.com/showthread.php?t=33857 For gps turn location on under phone and then disable agps is registry under. local machine-software-htc-supl agps set enableagps to zero. Now use htc gps tool or gpsviewer for lock info