Re: If, that,
I'm with 5jj. If you doubt something, then there are some alternative outcomes and you are not sure which one will happen (or has happened) therefore "whether" is fine. However, stating "I don't doubt ..." means that you already know the fact, the outcome etc so "whether" and "if" are not appropriate. For me "I don't doubt" means much the same as "I know for a fact" or "I completely believe", and can therefore only be followed by that.
I doubt whether [or not] he can jump over that wall.
I don't doubt that he can jump over that wall.
I doubt whether [or not] Obama is up to the task.
I don't doubt that Obama is up to the task.
He doubts whether [or not] the planet will still be here in 5 million years.
He doesn't doubt that the planet will still be here in 5 million years.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.