Posted from the link above:
How To Root Samsung Infuse 4G
To begin, download SuperOneClick from the link above and extract it anywhere on your PC.
On your phone, make sure USB debugging is enabled in Settings > Applications > Development > USB Debugging.
Now connect your phone to the computer and run SuperOneClick.exe and hit the Root button.
That’s it! Once the Root button is clicked, the rooting process will begin and once done, you should have a rooted Infuse 4G.
— modified on Sep 23, 2011, 5:14:36 PM