Asus p5qpl am support 9800gt ddr2

Assuming you have the PCIe socket on your motherboard then yes. You can run a DDR3 or DDR5 card on your board. You don't need to run DDR2 like your motherboard. The RAMs are kept separate, so no need to worry.

i have g41 with a slot can i plug a 9800gt yes or no

yes as long as you have PCI-E x16 slot (version 1.x or 2.0)

I was trying to point out you don't want to use a PCIe 9800GT if it has DDR2. Find a better card.