It seems the McCain campaign is out of ideas; instead they’re just making stuff up.
From Talking Points Memo:
It turns out that that “overhead projector” John McCain claimed Barack Obama tried to get a $3 million earmark for was actually money to rebuild Chicago’s Adler Planetarium, the oldest planetarium in the United States.
McCain’s “overhead projector” is the apparatus that runs the planetarium, which is a bit like calling the Palomar Observatory a new set of glasses.