I've never tried it, so no idea if it works, but I found this:

The following are suggestions for users with laptop computers:

Type as you normally would using your laptop computer. When you need to add a Spanish accent,

hold down your Shift key and press the NumLock key.
You should still be able to type normally on the keyboard.
Add the accent by holding down the Alt key and Fn (function) key and then use the secondary numeric keypad located in the center of your keyboard to type the numeric sequence code.
Once you are finished typing accents, you can toggle back to the regular keyboard configuration by pressing and holding down the Shift and pressing the NubLock.
Now you can resume typing.
Below are the numerical codes that correspond to the accented characters.
Alt + 0225 á
Alt + 0233 é
Alt + 0237 í
Alt + 0241 ñ
Alt + 0243 ó
Alt + 0250 ú
Alt + 0252 ü
Alt + 0191 ¿
Alt + 0161 ¡
Alt + 0193 Á
Alt + 0201 É
Alt + 0205 Í
Alt + 0209 Ñ
Alt + 0211 Ó
Alt + 0218 Ú
Alt + 0220 Ü
Note: On some laptops you may need to use the secondary numeric keypad that is located in the center of the keyboard when you type in the accent codes.