I know there was a thread asking how to do this but its been a year since that thread was replied to and I figured I'd just start fresh with a new one that explains how to do it.

The solution originally came from Stylus15 on the official Sims 3 forums.
Go to My Documents\Electronic Arts\The Sims™ 3 Create a Pattern Tool, then find the file named "Options". Open that file in notepad (or whatever text editing application you use..)

It should look a little something like this:

[Options]
ResolutionWidth=1024
ResolutionHeight=768
Windowed=1
RefreshRate=60

You need to change the 'Windowed=1' to 'Windowed=0' Then save the file.

Next time you load up CAP, it should give you a black screen with the word 'Loading...'
>edit<
It should then display your application in glorious full-screen.

You will lose your bottom toolbar and will need to hit Ctrl Esc or Quit to get out.

I will note that I haven't tried this myself just yet as I can't remember where I put the CAP program now and the icon seems to be gone from my desktop. I'm not sure if changing the window resolution would matter, but I suppose one could try doing that as well.

I hope this is helpful. If anyone has any feedback on how this works or finds that it doesn't work, please let me know.

still cant find the options file ;(((

I know this Q is SUPER old at this point, but here is what I found in (10 easy steps):

1. TEMPORARILY change your display setting to something more square, say 1280x1024.
2. Load "Tool".
3. You should now be able to see the (...) button in the bottom left corner
4. Tap (...) button.
5. Tap Options.
6. Tap to select the appropriate screen size (not even sure this is necessary actually)
7. Tap to mark "Enable Full Screen Mode".
8. Tap check mark for OK. It will go full screen right away.
9. Close "Tool"
10. Restore your display settings to normal.



I hope this is useful to someone in the future. Not sure how useful this tool actually is, though.