iphone 3g back replacement (how to)?

hey everyone, i have a 16gb iphone 3g model that i bought off of ebay a while back for about 210 dollars, the cheapness was basically becuz it had a slightly cracked screen, i replaced the screen with a kit i also found on ebay. that just included the digitizer and glass with all the tools to do this. It was fairly easy, at least for me.. and i had fun taking apart my phone! =] now i have a flawless screen. Becuz the iphone was very cheap and i had only a one time chance to get it, i got this one with a black back. I really wanted a white one, but now i am kind of leaning on orange. Anyway, i may be somewhat technically skilled, but i am VERY afraid to replace the back by myself, not to mention i really cant find any decent how-to instructions. And all the back replacement services are pritty expensive. So, if anyone has done this before, advice is appreciated and/or (clear) instructions on how to replace the back of the 3g. And if so, maybe a CHEAP iphone back replacement service, if those are out there somewhere.

thanks!

anything is appreciated!

longest explanation ever! lol