Vector lines to areas

        I have a vector file of lines only, These lines form a set of basins.
I need to make a mask such that there is only one or as many as the user wishes
basins visible. The problem is that since there are only lines, how to get
areas out of them and then I was thinking that I could make a mask by running
v.to.rast. Any suggestions ???

Nalneesh Gaur