I went thru it myself, here's what I did. Yes it may be a bit confusing, but once you figure it out it does work.
I used AnyCut to get a Diagnostic Access shortcut, otherwise MUCH harder trying to catch the phone in a specific boot state to perform this
Get AnyCut from the Market
In AnyCut, select New Shortcut, then Activity, scroll way down and choose Select COM Port Mode, click OK
You now have an Android-icon shortcut by that name on your home screen
Click that icon, select the Diag radio button, and it will close out
Connect the phone via USB
Open Device Manager on the PC and open the Ports drop-down menu
You should see a Diagnostics over Android listing, note it's Port # (mine's on Port 10)
Close Device Manager
Open QPST Configuration app on the PC
Click the Add New Port button
Choose the Port you found from the window on the left, click OK
Click on the port text in the window to select it, then in the top menu bar above the tabs click Start Clients, then choose Service Programming from the dropdown menu
A new Service Programming window will open, your port listing should be be selected, click OK
The window will change and you should see the listing in the top bar, and it should show it as online, meaning you are connected to the phone
Extract your new PRL file from it's .zip file where can find it on the PC desktop
Be sure you have a copy of the stock OEM PRL if there is a problem
Find the Roam tab, about the 7th one from the left, click it
In the lower left of this window, click Browse beneath the File box in the Preferred Roaming section
Browse to the extracted PRL file and select it
Click the Write To Phone button just below the Browse button, to write the file to your phone
If successful, your phone will reboot itself
Exit out of all the QPST program windows
When you phone reboots, you need to switch back from Diag to Mass Storage mode
Just open the shortcut you created earlier and select the Mass Storage radio button and you're done!
Hope that makes it a bit easier, after I figured it out worked well for me. Just a lot of steps we're not familiar with! :-!