If you are going to Egypt (and have not been before), it is more than worth your while to take some time to see the sites. You could spend all 2 weeks doing as much and not miss out...

But given you are there to dive (which is great; there is plenty of good diving in the Red Sea), here would be my "must see" list in Egypt:
1) Pyramids (d'uh)
2) Abu Simbel
3) Valley of the Kings
4) Siwa Oasis
5) Cairo Souqs
6) Egyptian Museum in Cairo
7) Siwa Oasis (maybe not a "must see," and to the west, but surreal.

Yes, it will be blasted hot in June. Drink lots of water.