I found that they actually had an option of instantiating the GT11CLK in some earlier version of the Architecture Wizard (http://www.xilinx.com/xlnx/xil_ans_display.jsp?iLanguageID=1&iCountryID=1&g etPagePath=17415), but it has been deleted in 7.1... Not very helpful... /Mikhail
The Virtex-4 lib manual suggests that the Architecture Wizard should be used, however I can't see how... The Virtex-4 RocketIO Guide doesn't seem to have this information either... Thanks, /Mikhail