The IP Cores developed by Altera/Terasic are still a Beta release. For the Beta release all C code has been created for and tested using the Altera Debug Client. The C code will not be fully integrated with the Nios II IDE until the full release (some time mid 2007). If you want to use the cores now, please use the Debug Client. If you want to use the Nios II IDE, you will have to copy the IP Core's drivers into your project manually, plus you may have to modify some of the code for it to work properly.
Best Regards,
- Blair
P.S. The Altera Debug Client can be found at
altera tutorials and exercises page (
http://www.altera.com/education/univ/materials/manual/unv-lab-manual.html)
altera debug client's installer (
ftp://ftp.altera.com/up/pub/altera_debug_client_setup.zip)