When I go to the monitor part of limewire and see all the people uploading files from me, I sometimes try to browse them. But, 80% of the time I can't; I assume they have that part of their program turned off.
I only browse the ones that have the little yellow circle on it because that is what I was told: If it has a circle then they are on the network and you can view their files.
I often thought about killing their download for not sharing. Would this be wrong? Or am I just not doing something right?

To my knowledge there's some unknowns as to why we can't always browse someone. Even if they have the chat enabled. And you're right, if they have a yellow chat icon they are much easier to browse. It might be due to you or them not having enough available bandwidth or something else. Just b/c you can't browse them doesn't mean they're not sharing. Personally I have my Preferencing set to a minimum of 30 files (Tools>Options>Advanced>Preferencing.) I presume this works. I do know the slider doesn't work.