You can install 2x4gb modules in dimmA1 and dimmB1. Slots 1 and 3 going left to right from the cpu.https://www.asus.com/Motherboards/P5P43TD/HelpDesk_Manual/
Remember only 64 bit operating systems will see more than 4gb ram.
I know about the 64 bit and 4gb ram. but thanks for the solution 1 and 3 slot!
I appreacite it!