Pull the original module and run with the two new ones and see what happens. You're RAM timings will always be those of the slowest module.
I started off with 1 gb Corsair XMS (2 X 500 PC3200) in my Asus P4C800-E motherboard with 2.4P4 CPU. Everything was fine until I added an additional 2 GB (Corsair Value Ram 2 X 1GB PC3200) in the remaining 2 slots. Now I see a noticable difference in all my apps - very slow!
What could be the reason? I am running Windwos Vista 32-bit.
Could it be the way the RAM is ordered in the slots? The sequence is