GTA IV running too slow

Hello,
i have just installed GTAIV on my laptop having specs as follows:
Intel Core 2 Duo processor T5800
4 GB RAM
nvidia GEFORCE 9500M (512 MB)

these are well above the requirements for the game to play... yet i am experiencing he game to run real slow and gets stuck too at times... im now confused as to what to do... i've tried changing the resolution of the game , etc.
i was pretty hopeful the game would work nicely on my laptop.. i'm using Acer Aspire 6920G....
kindly assist me as to what to do next...