Yes, you can Host Forums on DH. There is a nice and easy one-click-install of PHPBB. It's also very easy to install many other scripts on your own.
I don't really know for sure about what payement methods DH takes - but I can't imagine how else you'd pay... Enless you want to show up at their door setp with sandwhices and cookies and see if that works.
I do believe DH will accecpt any of thoes written in US dollars - but if it's a check you're going to have to wait while it clears the bank. It's definatly worth using credit card if you can.