I'd also like to give some input on the client you are using - it is OLD. There are much newer ones with bug fixes and more features. Here are a couple options:
The official client:
http://www.bitconjurer.org/BitTorrent/download.html
BitTornado (formerly Shadow's Experimental)
http://www.bittornado.com/
Azureus (Java client)
http://azureus.sourceforge.net/
ABC (Puts all downloads into one list box and is based on Shadow's Experimental Client):
http://sourceforge.net/projects/pingpong-abc/
I recommend you try all of these first before deciding on one. They all have advantages over others, but I'm sure one is right for you.
Changing the client may or may not fix your download problems. I do highly recommend you do not use unlimited upload unless you are on a T3 or better.