I'll try to answer your question about how to "go about" steelheading. As you might have surmised from the other posts, the general consensus is you'll need an 8-weight. I concur, though there are plenty of people on this forum who'll say you can get by with a 6-weight. True I suppose, but cantcatchem can apparently tell you a little about trying to get by.
Whatever rod you use, it should have a pretty fast action. In most situations around here you'll need to be able to cast a lot of line. I would say that if you can't consistently throw at least 60 feet, you're going to need to get pretty lucky to catch fish (you're going to need to get pretty lucky anyway).
You'll want a line with some kind of interchageable tip system. You can buy these or make one yourself. At best you'll want at least five tips, a floater, and then 10', 13', 17', and 20' sink-tips (all type VI or equivilant). This system will help you effectively fish about every set of conditions you find. If that's too much trouble or expense, get a wieght forward line with a 15' sinktip.
Good fly water is 3' to 6' deep, running about as fast as you can walk (3-5 mph), over cobble, the bigger the better. The most classic water is a short riffle that bends away from the bank about 15-20 degrees, leaving a band of easier water against the shore from 20'-60' wide. The sweet spot is generally thought to be the seam between the faster and slower water.
Start at the very head of the riffle. Cast about 20', about perpindicular to the current, let the line swing all the way around till it's straight below you. Staying in the same spot, pay out about 3' of line and do it again. Keep doing that until you're at your casting limit, then after each swing, take a step or two downstream and do the long cast again. Keep going until you've covered the run entirely, all the way to the tailout.
That's the short version. There are a lot of finer points about direction of cast, line mending, and so forth that you'll need to learn from experience to fit to the water in front of you. The thing you're trying for is a deep slow swing of the fly. Hopefully the fly will be deepest and slowest as it crosses that sweet spot at the seam.The trick is to keep at it, and try to be meticulous. It can get repetitive to the point of boredom. You have to get yourself into something of a "zone." Tom McGuane said the best steelheaders are the ones with strong arms and room-temperature IQs.
Around here, most chaps like big flies with lots of action, marabous, rabbit leaches, and the like in purple, black, orange, wine, pink, on #2-3/0 hooks, tied on a short leader (no more than 4').