> i'm wondering if the MorphOS hardware is just too slow to emulate a x86 pc
> designed to run a game which only needs a 486 and some memory or if the
> dosbox port is not optimized?

I guess the answer is a matter of perspective, given that DOSBox lacks an x86-to-PPC JIT compiler. You may want to have a look at those references:

http://amigaworld.net/modules/newbb/viewtopic.php?topic_id=32295&forum=32&start=60#672503
http://www.roylongbottom.org.uk/dhrystone%20results.htm

From there you can see that the x86 CPU that DOSBox emulates on your PowerBook should be performing somewhere between a 40 MHz 80386 and a 50 MHz 80486.

> can it be related to the missing opengl drivers in morphos?
> would that increase the performance?

I doubt it. DOSBox is a 2D application. Even 3D games running within DOSBox are rendered by the (emulated) CPU. I don't know if it's technically feasible to enhance DOSBox in a way that makes it possible for 3D software running within the guest system to have its graphics rendered by the hardware-acceleration infrastructure of the host system (like is possible with WinUAE for instance).