Ok this is what I could find for mac users, which is the same basic idea, just using different keys here it is:
For Mac OS, first hold down the Option key then a regular character key as indicated below. Nothing will appear on your screen at this point. Release both keys, and then type the letter which should carry the diacritical. For some special characters press Option and one key together. See the following table to get the character that you want:
Option + e + vowel = á, é, í, ó, ú
Option + ` + vowel = à, è, ì, ò, ù
Option + i + vowel = â, ê, î, ô, û
Option + u + vowel = ä, ë, ï, ö, ü
Option + c = ç
Option + a = å
Option + o = ø
Option + q = œ
Option + ' = æ
Option + s = ß
Option + shift + ? = ¿
Option + 1 = ¡
Option + n + n = ñ
Of, course you will have to do some fiddling around with different key combinations to come up with all kinds of characters not listed above, so try it out, see what you like.