You do not need LAA with win7 64 bit and the amount of ram you have.
This looks like an issue, if I am reading your information correctly, where the video aspects are not on a dedicated card. Check your listing in the Nvidia control panel and make sure that your GPU is selected and it is not set for AUTO.
Go to the Manage 3D settings and see what your system is using for the global and program settings. Under the Program settings for SH4 make sure it is not using global if you have more than one video connection or card and is only using the GPU from the Nvidia card. If your Global setting is only using the Nvidia card and the program is set for that then it should be ok on that end.
You will find a sticky with the best Nvidia settings for SH4
HERE because no one bothers to look.