Don’t be a middle-man between your graphic designer and your client. Be there for the first meetings between them. Make the designer write up a summary of each meeting and send it to all three of you. Once you know that the meetings are going well and that the summary is suitable to keep you informed, you can drop out and just read the summary emails.

You can join any meeting at any time if your designer and client need more management, either for scope, technical guidance, or other reasons. Projects move slowly enough as it is. The cost to everyone of “he said, she said” can be huge.

Maybe you double as an interior decorator, but even if you do, it’s really hard to convey to your designer that your client wants more of a peach-blush background than a warm pink, then get back to the client that the designer thinks peach-blush will wash out the key-lime highlight in the logo, and that it will have to be changed to more of a spring-grass-green, etc. Don’t be the middle man any more than you have to be.

I would think that you would act as a middle man or more like a project manager. you would get the information from the clients on what they want and then pass that information on to the designer. this way you know what is going on so that either you can tell him what you need for coding or you know what he is doing with it for when you code. this is very necessary for functionality of the application. if you have worked together a lot, then you would have a better understanding of what the other needs to create a good product and could determine, per client, whether it would be beneficial to have both of you there with the client.

you should have several iterations as well, so if need be you can bring the designer to one of the iteration meetings, which is probably what I would do in the given scenario.

You should act as the project manager on behalf of the client, gathering their requirements and managing their expectations, while passing as much information onto the designer as they need (it’s especially important that the designer be someone you know/trust).

I may be inclined to take the designer to the kick-off meeting though this should be decided on a per-project basis.
Once work has started, I’d bring the designer along to a couple of meetings (dependant on the size of the project) so they can get a better feel for your client, this will probably more important as the design progresses and becomes more finalized.

There’s always a certain amount of fluidity in these projects and some clients like to “tinker” with the design right up to the last minute, having the designer in the room can be a great help here.

I vote that you embrace design to at least some degree. Some introductory material that I like is included in a Mix 09 talk Design for Developers by Robby Ingebretsen. If I remember right, there is material in this talk about making a team that includes several specializations.

Many of the development tools are pushing toward templating a huge portion of the designers job, particularly the interaction designers job, on to the programmer, or at least into his tool set.

Whether your designer is your partner or a subcontractor, as a trained software developer and key stakeholder, your involvement throughout the process can insure that requirements are elicited effectively and scope is defined to produce a cost effective and rapid solution for the client.