First off all, download the V2 scripts here
if you haven't done that already.
Make a new folder in you main San Andreas directory called "Script V2" (I think you said that you've done that already) and keep on switching that with your V1. How you do that? Well, create also a folder called "Script V1" and copy paste the main.scm & script files (located in San Andreas directory --> data --> script) and paste them in your V1 folder. Now, you can switch them by either copy pasting each version from your V1 or V2 folders in the data --> script folder, and replace those files, or simply cut and paste.
Tell me if there's something you do not understand.