pretty much the only thing you need to do is set max upload in Limewire to half your upload minus a few KB/s. But there is no guaranty that you will be getting full upload on both computers though.

E.g. let's say your max up speed is 120KB/s. then make it 100/2=55KB/s on each computer. If you were to make it the entire 120KB/s divided by 2, then you might have trouble loading webpages etc. in case both Limewire's are using the full upload.