I know there are many people who don't want F1 to be help in AutoCAD. Courtesy of Lynn Allen, here is how to reassign your F1 key to be cancel, so it will act the same way as your escape key.
First execute your CUI command. In the upper left panel, scroll through and find keyboard shortcuts. Click on the plus sign to expand it. You should see shortcut keys and temporary override keys.
Next, in the lower left, you should see the command list. Find the cancel command. You can hit C and that will pop you to the start of the "c" commands, you should be able to find it easily from there.
Once you've found it, grab it and drag it up to the shortcut keys under the keyboard shortcuts. It doesn't matter where, as long as it is in the shortcut keys section. Click on the cancel under the shortcut keys to select it
Now, if you look over on the bottom right, you should see the properties for the cancel command. Click on the key(s) line to select it, then click on the ellipsis (you know, the three dots). In the box where it says Press the New Shortcut Key press F1. Click OK, and then again to exit to the CUI dialog, and your F1 key should now work just like your escape key!
Autodesk Knowledge Base and CAD related web sites:
ID: TS1055497 - Redefining F1 key to use Cancel command
AutoCAD 2005 or below: Changing the F1 key to Escape! via Lynn Allen
AutoCAD 2006 or above: Changing the F1 key to Cancel via Lynn Allen
Destroy F1 - in AutoCAD 2006 CUI
Disable the F1 key from opening the Help window?
Change the F1 function key to perform some other function