as rightly stated by Peterk12 Snow Leopard came with XCode 3 on its disk. There is/are Snow Leopard compatible versions of XCode 4, I am using XCode 4.0.2.
Downloading this is, normally, only possible in the Apple Developer Zone for which you - as also stated already - a developer account; which is free of charge though. No subscription etc.
According to this thread on the Apple Support forum, though, there is a way to find alternative downloads through googling with the "Google hack":
XCode 4.2 Build 4C199 "download"
Though these will not be official Apple sites/servers, and some of them might be a bit dubious. Considering that there is always the possbility of a Trojan being put in a modified disk image, this is at your own risk.