err.. when are you trying to open it? if youv'e just turned on the computer, allow everything to load in first, like antivirus and windows stuff.
- are you playing a CD in the drive at the same time?
- or music in the background?
- or downloading something from the web


if no to all these then your computer probably wont handle running Limewire - its probably just about hanging on as regards internet access.

Download speeds might be a result of the same thing - too small a computer.