Castling while rook is under threat.

If an enemy piece is attacking your rook, but not any other square that the king will pass through... such as a bishop on b2 and the pawn on g6... can you still castle?

No  problem castling with the Rook under attack. Only the King is considered.

No castling THROUGH check, OUT of check, or INTO check. As long as only the rook is involved, no problems at all.

Thanks guys, that's what we figured but I just wanted to check with some people too.

It's because you cannot 'check' a Rook... only a King.

I remember reading somwhere that Korchnoi once had to ask the arbiter (I think it was Lothar Schmidt) whether it's legal to castle when a rook is en prise. He said he didn't know because it had just never come up.