Tough as it may be, it might really be best to simply wait until you're somewhere where Apple has a retail presence before doing anything.
There are ways around it, but it wouldn't be legal in your particular case. It could be done, but it would be a pirated copy and should you choose to pursue that particular course of action then this discussion will come to an abrupt end because that sort of thing isn't tolerated here.
I'd also be a bit wary about trying to put more RAM in the system than it's designed to handle.
indicated that you did not know what the "box set" was. For some reason, if you call Apple and tell them that you want to upgrade from 10.4.11 to 10.6.x, they will tell you that you need to purchase the "box set"Perhaps that is where the believe comes from.
However, the OP was not under such an illusion, just the one poster who may have been informed by an Apple Store employee.
Especially on an older system, you never know what the results are going to be. I work as an Apple repair tech, and a good chunk of what I do is deal with older systems. And Snow Leopard will run pretty well on only 1-2GB of RAM.