First off, there are two methods to flashing to new roms.
USPL and Hard SPL
Basically your phone has software to keep from being overwritten. In order to flash, you need to bypass this.
USPL, is a software that will temporarily disable this allowing you to flash then. This is the safest way to flash to different roms. Some roms require a hard spl, so it depends on what you are flashing to. Here is a link that has the USPL link to download and how to use it.
Now, if you want to Hard SPL, you need to know this can brick your phone if not done properly. First, hard spl permanently writes over your phone basically unlocking it. This can be reversed, but there are other threads describing how to do that. You need to make sure your ipl is 4 or higher. If it isn't, you will brick your phone. Check this my holding the camera button down, and press the soft reset button (use the stylus and push it in the small hole on the left side of the phone.) Make sure you hold the camera button down until you get the 3 gradient colored screen. (I think it's red, blue and green). The top will say your ipl number.
First, download this file
It will contain 3 files you need to install first in a certain order. Unzip this to your desktop. It will make a folder called hardspl 6.
You need to make sure your phone has an option selected. Go to start\system\usb to pc. Check the box for advanced networking
Next, you want to put your phone in flight mode.
First install canonyang.cab.
(Install by copying that file to your pda through activesync and then just use file explorer to find the file on your pda and double tap that file).
Next install aserpolicy.cab
Finally install disablesecurity.cab.
Then do a soft reset (press the small hole with your stylus on the left side of your phone).
Now, go to the hardspl6 folder on your desktop, and run the romupdateutility.exe file.
It will walk you through the install. At one point, your screen will go white. Leave your phone alone until it reboots itself. Viola! You are hard spliced. Now, you can load whatever rom you wish to.
Hope this helps somebody out there...I was extremely confused at first.