TESTAMENT, from Green Ronin.
I'll say it again. TESTAMENT, from Green Ronin.
One last time, for absolute clarity. TESTAMENT, from Green Ronin.
Rules on being a Khery-heb (Wizard), Eqyptian Culture, History, stats for famous historical and legendary Egyptian personages, and Egyptian religion. Awesome resource, but one more geared for a fantasy campaign.
Alternatively, you can pick up GURPS Egypt. With an absolutely smothering blanket of facts, lagends, stories, etc. You can't go wrong with a GURPS supplement.
The downside is it's not d20, but it is reasonably convertible.