The zip file uncompresses into three files.
Two of them are .iso files, i.e. CD images, and for best results should be burnt to CDs.
Then, once loaded into your CD drive, the contents can be seen.
The installation can then take place, as Oldden has described, from the first CD.
The third file, a .txt file, contains the serial number.
How this got into the public domain I don't know, but once released to one, it's obviously made the rounds around the world.
I know, via the internet, the original owner of this copy of the program, and it's the copy of SOL2 that I use from time to time.
The program dates back form around 2003, i.e. before Windows 7, 8 or 10, and it's therefore to be recommended that you install it, and run SOL2, in Windows XP compatibility mode.
Since it's only from the early part of the century, it doesn't contain any of the .ini files for Yamaha keyboards, pianos, etc. from beyond this period.
Hope that's of some help?
Colin.
P.S. If you have problems with creating CDs from the iso files, drop me a PM and I'll see what I can do! ;-)