Thanks for the help, sorry for the delay in response. I ended up manually switching between the two. It was a pretty serious disappointment though because I urged the photographer to go with a mac, and it is unable to do what he needs. Windows 2000 on an old notebook could handle printing simoultaneously.
I tried giving the printer another name. Unfortunately, when I tried to add the second printer, it would replace the old name with P400. I didn't try that localhost thing, I'll have to give him a call and try it out. I believe the problem is with Olympus' drivers for OS X. The default name is given as P400, which is causing the problem. All Olympus would have to do to fix the problem is have the driver make the default name P400 and add the USB port number to the end of the name.
Things went alright, if a little slowly. Mac OS X using Photoshop to print and iPhoto as a database is great. This small problem makes the system virtually useless to him though, so I will endeavor to find a way to fix it and prevent a switchbacker.