theres a easier and fast way is by flashing by storage card. first make sure u hardspl ur phone this unlocks your phone so u can run custom roms.you can find that here
http://forum.ppcgeeks.com/showthread.php?t=93252. then download ur selected rom and extract to find the RUUsigned.nbh file. then rename that file to RHODIMG. put that on the root of your microsd. once you've done that you have to put your phone in boatloader phone by holding down reset button, power button and lower volume button. then it will ask if you would like to contuine by pressing the power button. then your done! just wait for it to finish and rest.
that link i gave you is for a cdma phone like sprint or verizon.
if u have a gsm phone like tmobile or att you need this
http://forum.ppcgeeks.com/showthread.php?t=80265