If you are going to use a peer to peer sharing program such as LimeWire, you should frequently defragment your hard disk drives & partitions. Such programs tend to fragment files quickly. A fragmented drive becomes slow. Also make sure your drives don't get beyond 75% full if possible. The fuller a drive is, the slower it gets to read. I would also recommend you do not download files to your system drive or partition. By not doing so you are lessening the chance of running out of system space, and also your system slowing down due to fragmentation & lack of space.

The limewire program takes up approximately 20 MB or less. Anything else is what you download or share using the program. After all, gnutella is a peer to peer sharing network. What files you find are what other people like yourself are sharing. If nobody shared, then there would be nothing to download.