You can only purchase content from the Connect Store via the Connect Software, which doesn't presently run on Macs.

There
was a rumor a month or so back that they might be thinking of portalling that software for MacPuters, but so far, nothing further.
You
can load files via memory cards, but we didn't have enough time to really get an idea of how livable that solution might be in the long run. I didn't really see anything that seemed too burdensome at the time, though.
It's only handles a
single DRM type until the reach some sort of agreement with another company (I agree, not real likely), or somebody hacks another reader app into it (perhaps a bit more likely).
Presently the only e-ink alternative handles zero DRM types.