I am new to this Android stuff. I would like to know the easy way to install a custom ROM on my phone. I have already rooted my phone.
The easiest way is through ROM Manager (you can find it in the Market). After installing it, open it and select the .zip file for the ROM you want to install. The phone will reboot into Recovery mode. Hit "Reinstall packages" or something similar to replace this recovery with Clockworkmod Recovery from ROM Manager (may have to do this twice). Then your phone will go into this new recovery and install the ROM.
Note you can also use a Windows tool call Odin, but you must have a ROM specifically designed for Odin. You might need to flash a "Clockwork compatible" ROM through Odin before ROM Manager will work.