Put some proper dry powder lock lubricant down the ignition switch.
http://www.tooled-up.com/Product.asp?PID=25141
Similar stuff is available from locksmiths, hardware stores etc.
Dont use WD40 or anything like that, it may make things better for a little while, but it will soon gum up and be worse than ever.
It is possible the ignition switch is broken and will need replaced, but try the lube first.
vaux, November 2010
