Bought WorldOfGoo on a similar thing before and it was just .exe download (yes, exe and zip downloads). And yes that's fun puzzle stuff, Gish should be the same and no idea on the rest.
You cannot complete this action on the card you have selected. Please select another card.
Never had any issues before, this with paypal. Something funky on this think if it's rejecting foreight cards? OP happened to have funds on paypall account?
edit: Success! Thanks for supporting the humble bundle!
So all that is needed to do is pay with card currency and let paypall do the conversion. I usually pay with dollars, as it's few sents cheaper