every time i click enable in the monitor window i get a message that says "Your client is a leaf node shielded by a ultrapeer. Hence you will see few or no searches in the monitor window"

what does this mean?

also why is it i can be downloading something at like 50/kbs then when i get up to 75% downloaded it stops and gets stuck on requery sent waiting, the counts down?

Recent versions of LimeWire use Ultrapeers to organize the network. If a computer has plenty of bandwidth and CPU time available, Limewire may select it to function as an Ultrapeer that accepts connections from a handful of leaf nodes. This process helps transfer traffic towards the computers best equipped to handle bandwidth and CPU requirements.

You can read more about Ultrapeers in the LimeWire FAQ:
http://www.limewire.com/index.jsp/faqs#sta7

As for your second question, this is probably happening because the user you are downloading from has disconnected from the network. Just as when you close LimeWire all uploads in progress are aborted, the same is true for the users you download from.

Hope that helps,
-Avi