All you have to do is to paste these lines into your hosts file:

62.210.142.5 swat4.available.gamespy.com
62.210.142.5 swat4.master.gamespy.com
62.210.142.5 swat4.ms15.gamespy.com

Thanks to Sun there is a video that explains how to do that in detail

If you can't be bothered to manually patch hosts file, you can patch game file called Engine.dll. Download the file corresponding to your game version then copy it into the Content/System folder (ContentExpansion/System for SWAT 4: The Stetchkov Syndicate) replacing the original file. Ensure to backup it first though!

• Engine.dll for SWAT 4 1.0
• Engine.dll for SWAT 4 1.1
• Engine.dll for SWAT 4: The Stetchkov Syndicate

More info can be found here.

Please check the Hosting a server guide on the master server patch page.