How much internal memory do you have?
Are you running in UltraPeer mode?

Slow speed may come from the fact that LimeWire now uses a bit more memory (but this can be greatly enhanced by using Java 1.5 instead of Java 1.4, because the 1.5 version has a much more efficient memory manager, notably a faster garbage collector to free up unreferenced/unused memory).

To help us, open the Options panel and click on the button to show an example of a "Bug Report". Then copy/paste the content of the dialog that appears.

Another reason may be that your PC installation (if it is a PC running Windows XP) has a problem within its UPnP installation. Consider disabling UPnP (and configure your router or firewall yourself), or check the UPnP installation: a problem can come cuased by viral worms that has attacked your PC, and steals you some bandwidth. So check for virus, and adwares...

And check for your general TCP/IP settings: notably slowness can come if you have a misconfigured or badly working DHCP server (in a defective router), causing your local IP address on your LAN to change too often.

If you don't use DHCP (determine the IP address automatically in Windows), check also that you have not assigned manually conflicting IP addresses on your LAN. Normally Windows should display an alert to you, unless you have disabled the Systems Messages service: in that case such alerts will be only visible in the EventLog viewer.

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