Learning the rules (with no experience of chess-like games) would be under 1000, I don't know how low though. It doesn't really matter how gifted you are if you haven't learned or practiced it at all. Think about it in terms of other skills.
I have two cousins that would play to pass the time as kids. No guidance from anyone, they only knew the rules. They didn't want to be better necessarily, only to beat each other. They played often, hours at a time. After a few years of this I'd estimate them around 1300. As you might expect their endgame and openings were bad, and tactics were the strong point.
Other than that I think it depends on what you want to call training. Playing every day with masters (who are friendly and analyze with you) would be great training. There are unrated players who are strong enough to be titled due to environments like this. People who grew up playing with IMs and GMs for years, and when they go to a tournament their first rating is easily above 2200.
Reading the issues of the day, has got me curious..
does anybody know whats the Highest FIDE/USCF rating for an untrained beginning chess player. perhaps someone in the late teens with big gifts and who picks stuff up quickly.