Hi!
After the Cet/Kerah scene in the pyramid, the game hangs up everytime if I want to enter the inventory/save/spell/map/... screen.
I am using Windows 98SE and the patched version of the game.
Can anybody of you help me, please ?

This is a very unstable area of the game. Try to give Kerah the holy water as soon as possible, without entering any screens. After she is restored the danger will pass again, though you might have to save and restart the game before it's stable again. Just hang in an save every few minutes.