I have spent 4 months on a project working extremely closely with a designer and he has still not picked up the basic idea of CVS (which is not my choice of source control system). I'm talking template files, JavaScript and CSS here. He's not stupid, it's just one of these things that makes his job harder so he resists fully commiting himself to it.
In my case I had to really hammer home the point that almost all of my JavaScript depended on the mark-up and when he changed his pure CSS, DIV-based layout into a table-based one without telling me then all my JS is going to break.
Often during the course of the project myself and the designer, who I get on with quite well and play soccer with outside of work, had very heated exchanges about our respective responsibilities. If I didn't know him well enough to just get past these exchanges then I think it would have created an unbearable working environment. So I think it's important you establish between you both and with some sort of manager or project supervisor exactly what is expected of both parties during the project.
In my case there have been very few problems lately, because the situation with CVS has been sorted out as well as the idea that he can't just go and change the mark-up whenever he feels like it. Rather than try and create template files and work on them directly, the designer only works on static files and its my responsibility to plug them into my template files.
It's all about communication and a little bit of compromise on both sides.
