You need to change the layout of your keyboard. Not to another one, but to a new one that has been modified by an utility like Ukelele (there might be others).
Download the tool, drag the App to your Application folder. Notice that in the Disk Image, there’s a folder called System Keyboards/Roman/, copy that to you desktop (it’s temporal).
Launch Ukelele and from the File menu select: “New based on…”
Open the file Spanish-ISO.keylayout (found in the Roman folder that you saved to your desktop).
You’ll see a big blue keyboard representing your current Spanish-ISO map (if you brought your computer in Spain, that’s they keyboard you should use).
Double click on the “,” that you want to modify (or any other key) and you’ll see this:
Replace the “,” with the “.” (dot). And go to Keyboard Menu -> Set Keyboard Name. Rename the Spanish - ISO to something like: Spanish - ISO2.
Now save it, the name will be Untitled, but you should put Spanish - ISO2.
Where do you save it?
According to Ukelele’s User Manual, you have different choices (and I suggest your read section 3.3 of the manual). Short answer is within the Keyboard Layouts sub-folder of the Library folder in your home folder. This can be created if it doesn’t already exist. If you do that, only your user will see (and be able to use) this Layout.
After installing the keyboard layout and logging out and logging in again, open the International pane of System Preferences (Language & Text on Mac OS X 10.6 (Snow Leopard) and later). On the Input Menu (Input Sources in 10.6 or later) tab, your new keyboard layout should be listed there. Enjoy your faster IP Address typing.