Wait, if I have 4 GB of memory, then why won't the game's free demo run? Is it something weird to do with dual-core processors or something?
Well, there's no guarantee that memory is the sole issue here. There might be some other incompatibility.
Anyway, according to your earlier post Windows detects 2GB, but HP list it as having 4GB. I'd say this is to do with your graphics chipset. A lot of laptops used a shared memory configuration, which means a fraction of your system RAM is allocated to the graphics chipset. There's usually a setting that allows you to change how much memory is allocated to graphics, but HP haven't documented any of the options in their setup utility, so I can't tell you what you need to do to change it.
I was able to find the model number for future reference though: g7-1017cl.