OK, About to take the plunge and flash my first ROM. I'm using SPRecovery and I understand that I rename the download to "update.zip" before I put it on the root of my SD card. However, I already have a file called "update.zip" on my SD from when I rooted my phone. Do I just replace the file? If so, will it cause me to lose anything? I'm being very cautious cause I'm a total N00B and I really don't want to hassle w/ a bricked phone!
You won't lose a thing. Once you have flashed an update.zip the phone is DONE with it. You can rename it back to what it was so you know what's what... or just replace it. MAKE A BACKUP BEFORE FLASHING STUFF so you have something to fall back on! That will prevent a lot of potential problems.