Xilinx ISE VHDL to Symbol

http://www.xilinx.com/itp/xilinx10/isehelp/pp_p_process_create_schematic_symbol.htm

Schematic overview
http://www.xilinx.com/itp/xilinx10/isehelp/ise_c_schematic_overview.htm

Related discussion: Conversion of VHDL code to symbol
http://forums.xilinx.com/t5/Design-Entry/Conversion-of-VHDL-code-to-symbol/td-p/29535

ISE quick starting guide
http://cseweb.ucsd.edu/classes/wi11/cse141L/Media/Quick-Tutorial-11.pdf