Batman Arkham Asylum Lag Help!!

So earlier today, I finished downloading the demo, and tried it out, only to find that I lag almost every 10 seconds.

I changed my graphics card from 9400GT to a GTS 250, turned off physx and played on low settings, but it didn't make any big difference.

Can anyone help me on this?

Specs:
AMD Athlon(tm) 64 X2 Dual Core Processor 5000
3.2 GB of RAM
NVIDIA GeForce GTS 250
Res: 1024x768

Please help!

If you mean the game's system requirments, the recommended settings are:

OS: Windows XP Sp2/Vista Sp1
Processor:Core 2 Duo 2.2GHz processor family/Athlon 64 X2 4400+ (required for MP host)
Memory: 2 GB RAM
Hard Drive:12 GB
Video Memory: graphics card with 512MB (SM 3.0). NVidia 8600 GTS or ATI HD 2900 XT.
Sound Card: DirectX 9.0c compliant
DirectX:9.0C
*Internet: Broadband (768kbit/sec upstream required to host 16 players)

Yeah. Thats why I'm confused too. Its like the same as my old 9400GT when playing Batman.

don't listen to them when ever you ask for help the always say you cpu is to slow, my old computer had an 4800+ with an 9800gtx+ superclocked and the game ran fine no lag at 1400res, the problom is your gts 250 that card is crap i had 1 when didn't rally run right, just get rid of it if you can and try to get a 9800gtx+ or even a 9800gt if you look on new egg lots of people run into all kinds of probs with that card