Hi,
Please try the folowing:
1. Search Google for "IBIS" or "IBIS specification" and You will find lots of interesting comments
2. h**p://www.xilinx.com/products/virtex/techtopic/vtt004.pdf (basic info)
3. h**p://www.eda.org/pub/ibis/
4. h**p://www.eigroup.org/ibis/specs.htm (specification itself)
Best Regards,
F.S.