3/2 with virtex 300

I don't have the vhdl handy at the moment.  You need to change your 
input buffer from an IBUFG to an IBUF to be able to place it on an 
arbitrary pin.  You probably don't need to place anything else, nor do 
anything else special.

Benoit,
You need to learn how to search Google groups! ;-)
Look here for example code:-
http://groups.google.com/group/comp.arch.fpga/browse_frm/thread/b2e060b33fd0a0a2/c1a2d891c6d6ca77
HTH, Syms