Playing with the numbers gets you virtually any combination you guys want of:
+ money injected into the company + money transferred to your cofounder to buy him out + resulting remaining cofounder diluted ownership of the company + resulting VC ownership of the company
Those numbers will probably be subject to contentious and highly consequential negotiation. Again, run it by your lawyer and, if you have them, other advisors that you'd routinely tap to discuss cap tables.
For everyone else, this is a perfect example of an irony many entrepreneurs face today: some investors won't consider investing in a startup with only one founder, but co-founder relationships can create all sorts of problems that sour (or even kill) deals.
Mark Suster had some great advice about co-founders at a Startup Grind talk last month. http://youtu.be/oAHgGUFjK3c