[Darkman]

There is a rather decent rogue guide at gamefaqs.com. The site is currently down for maintainence, but I remember that it had a section devoted specifically to building a rogue/mage. You should check it out once the site is back up.

BTW, you don't have to dual to a mage so to speak. You can make the change gradually, adding a level of mage here and there. I think the key things are to start as a rogue (for the first level bonuses), and then evaluate how much rogue skills you want and how many spell levels you want to have in the end. And of course, if you have high INT you should become a rogue/wizard, and if you have higher CHA then choose sorcerer.

Another note of some significance: a multiclass mage is not going to be able to cast spells all the time like a regular mage, so be prepared to develop your character so that he can fight when needed. You should definately take Point Blank Shot and probably some other combat related feats depending on your preference.

Good luck!