Urgent help needed: Photoshop and ACDC

[corinnacs]

I'm panicking, since I'm dealing with my first real paying clients--
The colors I'm seeing in my Photoshop screen are not the same as shown in ACDC. When I currently I'm looking at the proofing view in Photoshop set as working CMYK, When I change it to Monitor RGB or Windows RGB, it also changes the color. I can deal with the screen views, but what will the printed version be??? Which format is closest to what the web views will be and especially the printed version? Do I just send some in to be printed, and see the results?
The funny thing is, I never really noticed the difference until I did a shoot with some darker skin tones. That's when the difference in the warmer tones were noticeable.
Help!