If you only use Vista for photoshop & graphic tablet (one application), I would suggest you install Linux Mint and run Vista through VirtualBox. You can enjoy Linux Mint for all other applications with highest speed and security
And if you disconnect Vista from internet access, and don't install any other software, you can increase its speed also by running without anti virus software (but only if you keep it disconnected from internet and don't install any other software but photoshop).
BTW have you tried a Wacom tablet? I got mine to work with this help: https://help.ubuntu.com/community/Wacom
It works perfectly in GIMP also.