if you have ever worked on cars before you can do it yourself. There are tons of people on this board that have done the sr20det swap into a sentra. Hell, halfbaked and I can swap a tranny in under an hour now.
zeh, but tons, I mean like three, lol. check out
www.atl-sr20.com for more info about where to get motors and stuff like that.
If you decide you want to go with a shop, I would go with
www.batlground.com all the way. They're super nice and know what they're talking about when it comes to the SR motor.