You know your in trouble when you argue with yourself, talking is fine.
VA is volts x amps, transformers are rated this way as the windings are limited by current due to winding resistance, VA is used instead of watts, as the latter takes into account power factor, remembe the trans is limited by current so Volts x Amps is how they are rated.
So If your trans load has a power factor close to 1, you can work out the current by using the VA equation, if your using a switch reg then you can just use the o/p voltage as VA still applies at the transformer end.
I've confused myself a little now, thats kinda hard to explain, what I did was ball park by the way, power factor is never 1 and there are losses, but in practice its good to start with an approximation.