Hi Pierpaolo,
I don't believe your going to have much luck importing an ARCINFO DLG file
into GRASS. 
Why don't you use ARCINFO to ungenerate the vector layer and then import
this into GRASS. Take a look at the GRASS FAQ address for the procedure.
http://www.cecer.army.mil/grass/faq.html
Talk to you later.
Louis Clarke U.S. Army Corps of Engineers
lclarke@alb-co-r.swa.usace.army.mil Albuquerque District
voice (505)342-3281 Regulatory Branch
fax (505)342-3498 http://www.swa-wc.usace.army.mil/reg/