Need Nvidia GeForce 8600 GT Driver for My Manjaro XFCE

As @steanne commented you cannot use Nvidia drivers for your card - it is too old and unsupported by Nvidia.

You will have to use the Boot with open source drivers entry when booting the Manjaro ISO installer.

Sreenshot

When you have the system running on the open source driver - you may be able to get support for the Legacy card by following the advise in this topic.