Jackie, for a nice explanation on what bandwidth is, check ursula's posts here:
http://www.gnutellaforums.com/showth...6376#post86376
There are two different bandwidths: one for uploading and one for downloading. While uploading will help your donwload speeds, unless you're trying to upload to, like, a 100 peers (I'm exaggerating), then uploading won't slow down your downloads.
If you are disconnected, what you'll share is the uploads that were active at the point of the disconnection, meaning thatif you have 3 uploads and disconnect, you'll still upload until the uploads are finished, cut-off or you quit LW.
From that point of view, disconnecting will cut off other incoming seaches and also outgoing searches (you won't be able to search).
By "when Limewire is off", I suppose you mean when you have quit Limewire? In that case, Limewire won't upload or download anymore. Think about it: it's almost like asking "If my Mac is turned off, how do I know that it's not still running?" Weird, huh?
As for the Firewall thing, with the two Firewalls up, go to Limewire's Preferences, and click Bug Reports. Click the button to get an example then scroll down to the part where it says: "recieved incoming this session". If it says true then your firewalls are not blocking LW. If it says false then they are.