These commands are
fastboot commands, which like adb, is a program that allows you to interface with your phone from the computer. The difference with fastboot is that it's designed for low-level communications (firmware, specifically).
You need to reboot your phone to the bootloader to use fastboot commands. The bootloader is the "white screen" with text on it.
I think that if you're having to install an old ROM to get it working properly, then something has gone awry. Updating your profile with Virgin Mobile on your new ROM *may* help.
You do not need the whole Android SDK, you just need the
SDK Tools. You cannot open these directly by double-clicking on them. Press the WINDOWS KEY+R on your keyboard, and type in "cmd". Once your command prompt is open, you can type [high]cd C:\sdk-tools[/high] to go into the folder with adb and fastboot. From there, you can issue the commands I gave you above. Of course if adb and fastboot are in a different folder, you will have to "cd" (change directory) to the correct location.