Learning to play high stakes

[AceofSpades]

What is the best way (without blowing a substantial sum) to learn higher stakes poker? I know that sounds like a dumb question, and that experience, natural poker skill/mental facilities, and studying help. But what would you suggest as a good way to sharpen your poker skills and gain experience so that I'm able to play at the higher levels? It seems like levels 4/8 and up are seriously different games. Are head-ups tournaments comparable? I thought about buying in short and rat-holing but I know that this really cuts down on your ability to manuver post flop and that is a large part of the skills needed at higher stakes.
I guess the basic question is how to play against very aggressive LAGgy opponents willing to make moves and put you on a decision for all your chips?

So any suggestions?