I just ordered and installed a new set of wheels/tires from Tire Rack. The tires were already mounted and balanced. It was my first time doing this (installing wheels), but everything seemed straightforward. When I was finished I noticed a small amount of oil/lube leaking out around the edge of each tire/wheel. I am guessing that they use lube when installing the tire over the rim, and this little leakage I'm seeing is normal. Still, I figured it couldn't hurt to ask, even if it is a stupid question. :-)
What you are seeing is the remnants of the lubricant that was used to intall the tires in the rim. It should stop in the first few miles. If the appearance bothers you wipe on any one of the many tire gloss products available at auto parts stores and the streaks should disappear.