I just voted in Madison, and even though there were clear instructions about this posted in the voting booth itself, the ballot was still a little visually confusing.
If you are not voting in a senate recall race, you may cast TWO votes – one for Governor and one for Lt. Governor.
If you are voting in a senate recall race, you may cast THREE votes – one for Governor, one for Lt. Governor and one for Senator.
If your ballot is rejected by the machine because of an over-vote (voting for too many candidates), you may ask election officials for a replacement ballot. You may also ask for a new ballot if you make a mistake before inserting the ballot into the machine.
The Wisconsin Election Protection group says this:
“You only get to vote for ONE candidate for governor. NOT one per party! You CAN vote for different parties amongst the races (i.e. a Republican for Governor and a Democrat for Lt. Governor), but only one candidate per race!
“Any questions on voting? Our attorneys are standing by here and at 1-866-OUR-VOTE (1-866-687-8683) or tweet them @EPWisco!”
Wisconsin Citizens Media Cooperative 
Thanks for putting this info together, Rebecca!