Hi
you can do the integration with AX from CRM or vise versa depending on the requirements of yours, it can be one way or two way.
1. you can leverage CRM SDK, Webservices and Filtered Views to access and modyfy data on AX side. On AX you can always write custom Code to access data from outside word using AOT and other libraries.
2. In CRM you can Access AX data using the AX webservices and SQL access to database.
for the reference please refer the link below.
http://blogs.msdn.com/b/crm/archive/2006/07/05/657214.aspx
There are also third party integration helpers available to do so.
http://www.scribesoft.com/microsoft-dynamics-ax.asp
http://www.greenlightbts.com/company/press-releases/release-01052011-dynamics-ax-crm-connector-released.asp
AX SDK and documentation.
http://msdn.microsoft.com/en-us/library/aa493463%28v=ax.10%29.aspx
http://msdn.microsoft.com/en-us/dynamics/ax/bb453258
let me if you wanted to know in more details, i hope the pointers are sufficient.
Thanks, Bharatkumar. Save Nature For Future.