HOW to turn a Sprint Mogul into an ALLTEL 6800

Total noob here. I know nothing about Moguls. Just got an ebay Mogul in the mail today and need to turn it into an Alltel phone for activation.
There's TONS of info out there, but after swimming through it for hours, I still feel dumb.

Can anyone boil it down a bit for me?

I keep seeing that I can't just flash the Alltel rom from HTC's site without bricking it.

So what do I do? I don't want to try activating it until it's Alltel-ified.