The nvidia page you linked to says links to says this:
If you look in the "upgrade today" section it says:
The following Quadro professional solutions are required to accelerate the new Mercury Playback Engine in Adobe Premiere Pro CS5:
> Quadro 5000*
> Quadro 4000*
> Quadro 5000M*
> Quadro FX 5800
> Quadro FX 4800
> Quadro FX 4800 Mac
> Quadro FX 3800
I'm fairly certain you need a Quadro. Nvidia has a nasty habit of milking its customers for everything they can get.
I read before that the previous version of Premiere only supported GPU accelerated encoding on Quadros with the Elemental plugin, so much so that you could get a 'deal' on the Elemental plugin and a Quadro CX (specially designed for photoshop).