It is difficult to ascertain why sometimes we can browse others & sometimes not. It helps if they have chat enabled. Particularly those that are uplding from you. But just b/c you can't browse them does not mean they are not sharing. It might be busy traffic, it might be the vendor type, they or you might not have much bandwidth left over to allow it, etc.
Browsing is not the 'whole' point of p2p but it's certainly a nice xtra.
Try direct connecting to them:
http://www.gnutellaforums.com/showth...threadid=31572 & perhaps:
http://www.gnutellaforums.com/showth...threadid=31006 by Stief who is wise about this topic of browsing.
More about chat here:
http://www.gnutellaforums.com/showth...threadid=30911