I haven't tried that, but i'll let you know another option of a synthesizable uP for FPGAs, which is the LEON. It's freeware and has good support. http://www.gaisler.com/cms/index.php?option=com_content&task=section&id=4&Itemid=33. They have versions for specific Xilinx FPGAs. I know that there are specific development boards for the LEONs with Xilinx FPGA's installed, but i think it can be used on standard FPGA development kits, although i'm not sure.