DSL In A Small Business Environment

I have 2 clients that are looking to brinf DSL into their offices. Although I have installled and configured DSL in a home environment I have not done it in an office environment. My concern is running DSL in an office using a phone system with multiple rolling extensions, fax, etc. all on the same physical phhone lines. Do I need to require a dedicated line/jack with just the one DSL phone number on it, or will any jack in the office do? Any other things I should be concerned about?