I had to make some changes in the firewall of my antivirus. (if running windows XP)
if you have windows firewall and another firewall, you must deactivate windows firewall. they will conflict and cause problems with the internet connection.
right click on the network icon (in the tool bar) or go to open network connection. right click on your network adapter for your laptop, select status. Click on properties, go to the advance tab, click on firewall, turn off windows firewall, then go to advanced, uncheck both wireless and wired network.
click ok. so windows saves everything. Now, you antivirus firewall..you should have an option where you have to make your antivirus trust you network (private or local).
Check the website for your antivirus and they should have some information on how to do it.
I have four computer connected wirelessly to the DIR 615 plus two wired items (tivo and vonage). It works pretty well.
Also, are you behind a modem with that router? if so you have to deactivate the DHCP on the modem and make the connection as bridge. You should also be able to deactivate the DHCP of the router, which would act as a wireless access point.