first steps to print map from vector data in grass

Hello,
I'd like to produce a map from available vector data of read segments.
The result should look similar to Google Maps.
I know that it will require a lot of work, but can you please advise
me with the first step, namely how I can visualize a vector file
representing roads of different type?
I plotted the roads net using d.vect, but then I'm stuck. How do I set
the line color and the line thickness according to the road's
capacity? Do some grass scripts exist for this kind of job?

Thank you
Kim