Unexplainable Hardware Lag on Dell 531s

Hi! 

Thanks for taking time to read my post here.

Real quick I own a Dell Inspiron 531s (slim case) 32 bit WINDOWS VISTA.

I'm having a confusing and most frustrating hardware lag.

Two instances where I know this lag is created is when I run the electric sheep screensaver and FFXI(which can run on nothing) I can take the hardware settings for the game and put them at minimal and this lag will still happen. It is not internet related, as it does the same thing on the screensaver.

Now, I just updated my ram from 1 gig to 4 gig, put a new graphics card inGF 8400 256 MB supporting 512 MB DDR2 (copied off box), as well as anew dell monitor s2409w.

This lag itself is almost rhythmic. It will lag for about half a second every 2 seconds. this rhythm never fails. It's like it's falling behind and can't keep up. It did this before  (on board video card) and after (the video card (gs8400) update.

I figured at least the ram and new video card (which was recommened by my service tag entry on Dell's product page) would maybe fix this weird lag glitch. but it didn't. in fact i can't even watch internet videos now. even now after my video card upgrade, it's hard to watch videos on the internet (i did bump my res up to 1920x1080). Can it just not handle that? what else do i need to make this system usable?

I'm really at wits end here. I thought these upgrades would for sure help, but it seems like i need a bajillion megs of ram and what not. then again i have no idea.

Do i need to ALSO upgrade my processor? it's a AMD Sempron Processor 3600+  2.01 GHz

Another note; my system rating was also taken from a 3.0 to a 3.4 after my upgrades. (was hoping for a little higher of an upgrade) :/

Any and all help/replies are greatly appreciated.

Thank you so much.

Justin