I have not experienced any problems with having the .NET framework installed on the same server as ColdFusion. I am assuming you are *not* planning to use the .NET features builit into CF.
I would be more concerned with the security risks involved in putting accounting data on a web server rather than a file server which is isolated from the Internet by a firewall.
Thank you for the information. We will not be using the .NET functions in CF9. Regarding the QB data, the server web site is a password-protected login to a database and has no "public" web pages in the sense that just anyone can view them. We will soon implement a feature of the firewall to require logging into the firewall with a separate user name and password before port 80 to the database even gets opened, and that will prevent port scans from ever seeing port 80.
RDP to the server is already done that way, requiring firewall login before 3389 gets exposed to that user (me, and the CF9 programmer).
I appreciate your help!