If just one side of ur brake is touching the wheel you can try adjusting the center alignment using a small hex wrench and adjusting the small screw on the top of the calipers.
go here for some instructions on other brake adjustments
http://www.parktool.com/repair_help/...ualpivot.shtml
parktool's site has a lotta great bike faqs that seem to be useful
http://www.parktool.com/repair_help/FAQindex.shtml