Do you have multiple AD domains ? If you have multiple AD domains, with CRM users in a different domain from the CRM server, then the domain functional level may be relevant.
If not, then I think you should be OK, but you won't know till you've tried. A set of tests is:
- Installed CRM
- Add a user
- Check the user can access CRM
- Check the user can run CRM reports
Microsoft CRM MVP - http://mscrmuk.blogspot.com/ http://www.excitation.co.uk