If it's an ERIS they have a 1 click root. http://forum.xda-developers.com/showthread.php?t=742228
All the guy asks is that if you use it and like it, support some type of youth outreach or make a donation. (Honor system)
Works very well and the script even does a backup for you in case you need to roll it back. I found it in the nandroid folder when I was making a backup for XTRSense.
If it's another phone just cruise around XDA. Lots of good info and all of the more popular phones usually have a very simply rooting process.
Also it's definitely worth checking out the rollup thread. http://forum.xda-developers.com/showthread.php?t=756775
It basically has everything you'd need to accomplish backing the phone up, changing roms, rooting, and links to quite a few ROMs. There is also a detailed way to root the phone if you prefer to get your hands dirty.
If you want to take a stock phone and load a rom to it, you'd need to do the following steps.
1. root the phone
2. flash amon recovery
3. make a nandroid backup
4. download and install your rom