Do they actually get all the way in and then lag out? Or are they not able to get fully connected? If it's the later, you might check a couple of things. First, make sure they are updated to 1.03 if your server is also updated and vice versa. You might also check to see what you have sv_timeout set to be. If it's low, say below 60, then I'd increase it up to 120. If it's the former, I'd be curious if you are connected first/also. If so, try letting them connect without you. Then, when you connect, if it goes to hell, then you know that it's a rate problem between the server and you as a local client.
"Do you expect me to talk?"
"No, Mr. Bond, I expect you to DIE."