First ToDo if you have connection, lag problems.
 

I will leave this thread open for a while, and will stick it to the top. My goal here is to suggest all the basic first-timer solutions, so they can verify this thread and not have to search.
Here's some pointers (snippets from my old posts);

What kind of a ping do you have? you can have the fastest connection in the world, and also have a slow ping. Playing Everquest (from the client) does not require a fast connection, but does require a fast "ping". Believe it or not, modem connections usually have the best pings.
Anyways, here's something I've been using for years now, that helps optimize any type of connection.
http://www.speedguide.net/downloads.php (TCP Optimizer)

if you want to learn more about all this ( and you should) I found this link very helpful
http://cable-dsl.navasgroup.com/

Cable-internet users share bandwith with Cable-TV viewers - a lot of Cable-ISPs exploit this to a point that when the viewer traffic gets high (usually at night), it begins to slow down your connection, sometimes to a crawl.

Did you check for Malware, crapware, virus, etc? you did? then try again! this time use this;
http://www.superantispyware.com - free
http://www.ccleaner.com - free
http://www.weebroot.com (Spy Sweeper) gives you one free month
get all three, install/run them in detail - each has its unique features.

You can also run msconfig and look at what's in your startup and what services you have - disable ones that are wasting your bandwidth.
This link taught me how to do that;
http://www.onecomputerguy.com/window...rvices_disable