fayfay asked the right question.. if you are trading it in for insuranse purposes you may have to downgrade, which can be dangerous.
thread about dangers here:
http://forum.ppcgeeks.com/showthread.php?t=26082
Regardless of what Official Rom you flash to, all the official roms are windows executable files and all you need to do is download, activesync, and run the program.
After you have the rom, you may need to relock your phone.