Hi Kristan,
I'm on Linux reseller hosting myself and it should be easy for you to set up different accounts for the seperate domains on the server. Regarding the MS Access things, I can't think of the best solution off my head.... Obviously if you were planning on running it off the server, you couldn't do that but if the file was just for reference, you could download and people could then look at it (providing they have access). I'm guessing that's not what you want though.
I'm sure someone else will come along with a better solution than me. I'm currently recovering from my first day back at uni so I'm not quite with it!
