Mac OS X (10.6.3)
Use Software Update or the OS 10.6.8 combo update to update your OS. Also, update everything SU has to offer for your computer. When done, repair permissions and restart your computer.
Try the basics first:
Change your router channel number. Most times this works & is all you have to do.
Disconnect & reconnect your modem. unplug it for about 10 seconds. Plug it back in. Do the same for Apple’s routers. Wait for everything to reboot.
Click the Assist Me button.
In the next window that pops up, click the Diagnostic button & do the necessary.
Research Knowledge Base for network problems that pertain to the OS that is currently installed on your computer. See these basic networking KB Articles: http://support.apple.com/kb/HT1401 AirPort troubleshooting guide
http://support.apple.com/kb/HT4628 Wi-Fi: How to troubleshoot Wi-Fi connectivity
http://support.apple.com/kb/HT2712 Using network locations in Mac OS X
http://support.apple.com/kb/HT1714 Solutions for connecting to the Internet, setting up a small network, and troubleshooting
Also, run the Airport Utility app which is located inside the Utilities folder.
If using Apple's Airport, please re-post over in one of the AirPort Forums.
\Where do we get this combo update thing from?
From Apple's download site or from Knowledge Base. CLICKY CLICK -----> Mac OS X 10.6.8 Update Combo v1.1
Can't connect to internet so how to even get the update
Yes you can if you connect through ethernet. You made no mention in your original post that you are unable to do so.