Set up for business?

[newmacmom]

A friend and I have been making slideshows in our spare time, and it has turned into a side business. Right now, we are using two macbooks and an external hard drive, and it is working ok for now, but I am seeing how if we do this long term, we will need more. What would be the best set up to make sure the slide shows are backed up at least temporarily, the discs do not take too long to burn, etc.?

I was thinking about an imac--is the 2.8 really that much faster than the 2.4? The price difference seems huge (even when upgrading to 2GB RAM on the 2.4)? What if we wanted to do some video editing in the future as well?

Thanks!