Like Randy said, just pick apart the weed bed. I fish heavy weeds all of the time but you have to look for open spots. The walleye love sand and rock under them. If I see a fish on my locator that is sitting on top of short grass they are generally bass or panfish. I think finding these open spots is more important than technique. I could throw a jig/minnow, a leech, a plastic, a rippin rap, a drop shot rig anything that walleye normally bite and I could make an infomercial for it.
Fish hold tight to cover when they are in a negative mood so you have to be within inches of the tall stuff but not in it or you snag weeds, that is the key in a nutshell. The pic below took us two hours last night. An hour of searching for the right spot full of fish and an hour to catch over 25 walleye 15″-20″. We used minnows, leeches and just to prove it to myself a couple on a rippin rap and a jig and plastic.