While the Mac Mini has an "adequate" graphics card, it is nowhere near close to being suitable for what you are attempting.
I'm not sure I would be using the mini for this purpose either although you seem to be working it with some success. Isn't the HD a little slow?
I have just been reading through the system requirements for Motion 2 and even if you had a supported graphics card, your machine is marginal at best.
One of the iMac G5 series would be more suitable, PMG5 even more so, and the investment in software is still viable. Asking the lowest end Mac to accomplish your goal here is pushing the envelope. It speaks well for the machine, and OS, that it is actually giving you results.
To answer your question, there is not such a thing as an external graphics card for the Mac.
Hello, I am currently using a Mac Mini with 1gb of ram and 80 gig hd. I use it mainly for video editing with final cut pro 5, mix with soundtrack pro, and author with dvd studio pro 4. I recently bought Motion 2 and noticed before i opened it that my graphics card does not support the software. ATI Radeon 9200 32MB is the card i have in the mini. Is there such a thing as an external graphics card that I can connect via firewire? i have just invested a lot of money in software and hardware for my mac and i do not plan to buy another.