Originally in the aspect of putting Dayton Rims on an old car, the term has grown other aspects.
In all usage, the term is used to describe making something better with a bit of cash flow. Such things are used every day, from tipping a waiter/waitress so one may accquire good service, to putting money into one's computer network to make it better.
"I had to throw some D's at that sucker just so he could serve me"
"Man, that's one shitty cell phone... you aughta throw some D's at that, sucka!"