Liverbird

Lagging can occur when you use the game during "peak times", say when all the kids are in from school and all using the internet ---- you broadband connection will be slower at these times.
Other things to consider are background programs --- have you left the likes of Limewire running, some people are unaware that when closing Limewire with the corner "x" it minimises to system tray and is still running!
Users could be draining your bandwidth because you are uploading to them as they share your files.

Also check that an anti virus program is not running a scheduled scan in the background.
Windows Defender is a pain for causing ingame lag when it runs its daily quick scan!

*make sure you have all windows updates up to date too,..
Just a few suggestions

Liverbird :-)