using transmission torrent client behind a proxy

[Tapas Mishra]

I should not be asking this question as it is a straight forward thing
but the situation where I use my machine.
I am having internet connection in an environment whose proxies I do not know.
In firefox
Edit->Preferences->Network->Connection-->Settings --->Use system Proxy
settings option is there.
So I have not given any IP or port combination here and my Internet
works very smoothly.

Now here is a situation I wanted to download some Linux DVD's and I
used Transmission
since I have no proxy specified in Firefox so I thought it might
work.Which did not happen.
I checked
Transmission-->Edit-->Preferences-->Proxy

I have no clue as what value should I enter here.(Since the
environment I mentioned has given me a direct Internet access.
So if I want to use Transmission on port 80 (in above scenario)
what should I be doing?

Since Firefox uses System Proxy settings and in one day I am at
different places(different organizations)
 each place has a different network environment but I have internet
working each time (without any change to any Firefox settings)
so if I want to use Transmission also simultaneousy (in a situation
where I am not aware of proxy or proxy does not exist but rest ports
are blocked)
then what should I be doing?

-- 
Thanks
Tapas