The same copy of the game works fine in another system with no audio stuttering ... with the folowing specs
Pentium Dual Core
I like to laugh at people who have pentium 4/d cpu's on netburst architecture as it is power hungry and slow.
Pentium dual core are just less cached core 2 duo's 2-3x better per watt then crappy pent d. Anyway its most likely your cpu. I always see pentium d/ pentium 4 computers run like slideshow as the cpu can't keep up with the graphics that looks nice but cpu runs it as fast as the cpu can go.
Heck my p7350 2ghz c2d 25w ulv type cpu 3gb ram 320gb hdd 9600m gt 512mb gddr3 runs batman arkham city on highest setting at 1280x800 at 35-45fps with no aa.
i dont think there is a need to patch the game if it works perfectly on another system
The other system cpu is probably at least 80% faster. Pentium d with faster gpu will mean good graphics but physics will run slow limited to slow cpu. To be honest you should put the gt630 in the pentium dual core system as it should be a lot faster. pentium d is ancient cpu and power hungry. Netburst cpu and playing games with any gpu is slideshow as cpu cannot keep up with gpu.
arkham city plays on my p7350 2ghz c2d at 35-50fps on high setting at 1280x800 and my cpu is a ulv type p series 25w cpu and the slowest version. Baring in mind I have a 9600m gt. IMO arkham city barely requires much cpu or gpu power, similar to dirt 2/3 or driver san francisco all playable on high settings at 1280x800 at 35-50fps.