What TM is saying is that you have to buy Snow Leopard first, because the only (well almost the only) way to get Lion is to get the Mac App Store, and you need Snow Leopard for that. You COULD buy a Lion USB key for $70 and jump up directly but why spend the extra money?
Speaking of extra money, the later iLife apps (iMovie, Garageband, iPhoto) won't be included with Snow or Lion and your old ones may "break" depending on how old they are. You can buy the updated titles from the Mac App Store for $15 each, which allows you to only buy the ones you actually want. Nice.