I've looked at 2 other different images of this dialog and yours is different again. I honestly don't think you will find a solution. You can try Google as I have had a quick search and found a couple of pages with the same problem neither had a solution.
You could try another version of the driver
, Fujitsu has a Vista driver, a much earlier version that might have this option but it may not work with Windows 7 and theres the chance the ALC260 doesn't support this feature. You'll find that driver here Technical Support pages from Fujitsu
, just put your serial in the box provided, click continue, select Win Vista and Win Vista again, select Audio and click download on the right.
Otherwise you could live with it and like me (even though I have that option) turn off the speakers or unplug the headphones depending on which one you are using.
Let me know how you go but I have to go now I'll check back tomorrow.