Rose Pruning...of old roses

[lupine at pacbell.net]

I love to prune roses, and I can prune them to where they look really 
good.  I ran into a problem that I could use some help on.  I have seen 
many roses in my neighborhood that are very old.  The roses are also 
neglected, and have been pruned by people who know nothing about the art 
of pruning.  I was wondering how someone would approach pruning a rose 
that has two very thick, old canes.  The form of the rose bush is in the 
shape of a Y, with all of the new grow stemming from the tops of each of 
the old canes.  What kind of advice would you have for fixing the form of 
this rose bush, and giving the plant a chance to thrive and produce new 
canes?
Jen B.