The lad in the store was correct, but Apple was giving you the official way to do it (and not out of greed -- they don't sell Leopard so they make no money on going the "long route").
You can, in fact, jump from Tiger (10.4.11) to Snow Leopard by buying a retail disk (about $30). But be VERY AWARE that you'll also need to upgrade a fair chunk of your software if you haven't done so, so you should budget for new editions of the iLife apps you use, the iWork apps you might use, an updated copy of MS Office if you use that and so forth.
Apple's official solution is still, I think, the "Snow Leopard Box Set" which includes Snow, the full iLife suite and the full iWork suite. If you use more than 2-3 of the iLife apps, this is probably a good deal for you if Apple is still selling it.
Once you've upgraded to Snow Leopard, you have the option (not mandatory) of upgrading to Lion later on, though if your machine is as old as mine (2007) you may just want to wait until you replace the machine, since you'll get Lion as part of that.