i forgot to add one thing. using upnp slows down the windows os.
example: three days ago we finally tried the latest bittornado. after connecting for 4 torrents simultaneously i got about 400 halfopened connections on 4 incomming ports and 200 on few outgoing ports. using upnp at that time our winxp slowed down to such extent so we couldn't start even a wordprocessor. aftewards we've disabled upnp. under heavier load then previously winxp was running smooth. almost smooth like a baby cheek
the only problem was that our router couldn't stand the load and crashed very cruel. today morning we've patched the router software and it's ok till now.