Stay with Win 7. Running L2 with a resource hog OS like Win 8 on an old computer will probably not look good as you want it. Or, get a new computer and claim tax exempt/deduction like most of the people that are populating the servers.
With the amount of money you paid into the game, I seriously doubt your computer is as old as the OP. Didn't the Core 2 Duo and Geforce 8600GT come out in '06. In fact, OP didn't specify if his computer was a desktop or if his GPU was integrated. These things do have a surprising impact on how L2 runs when he upgrades his OS to Win8.1.
With the amount of money you paid into the game, I seriously doubt your computer is as old as the OP. Didn't the Core 2 Duo and Geforce 8600GT come out in '06. In fact, OP didn't specify if his computer was a desktop or if his GPU was integrated. These things do have a surprising impact on how L2 runs when he upgrades his OS to Win8.1.
Well,
I am waiting for skylake processar at the next year and I will make upgrade on my computer.
All people help me with this question, thanks a lot.