If a job's worth doing, it's worth paying someone to do it properly.
The 3 ipod touches in my household have all been taken apart DIY stylee, and had various bits replaced at some point The ones you see on youtube have all been opened previously, which makes it a hell of a lot easier. My first couple of attempts resulted in forking out for new screens to replace the ones I broke, and various other bits my sausage fingers snapped.
If you have the patience, a delicate touch, and a bit of spare time on your hands then go ahead. If you know a bloke on the sunday market who can do it cheaply, pay him to do it. Once they have been opened they are rarely ever 100% again.