I've used the iPhone since it's first release in 2007 and was very careful never to Jail break it. Come 2010 and Gen4 I got the funny curiosity to Jailbreak it myself. Believe me it was as easy as taking a walk in the park. (I am no computer geek either).. IF your question is whether the warranty is lost? the answer is YES.. BUT there are ways around it, you can restore it back to the original settings in minutes. :) So, no fret. Yup! it can be done and Yup, you can have all the fun with it as well. Let me know I can help. A word of advise, DO NOT upgrade to the latest firmware ie: don't download the new version of software and sync with iTunes..... believe me it is not rocket science, all that you will need is a decent internet connection speed and 2 - 3 hrs of patience.

Cheers!