I am looking at buying a Slim HP Pavillion and it has a...

[tomtoon]

ATI Radeon HD3450 in which I want to upgrade.

I've found the "low profile" cards as they are called for them.(9600GT I found)

I was wondering how to install it, if anybody knows.

[glc]

Before you upgrade the video card, you need to see if the power supply meets the minimum recommendations for a stronger card. I highly doubt if it does. It is not wise buying a slim PC to game with. The power supplies in them are generally low power proprietary form factor and are not upgradeable. You are much better off with a standard ATX tower or desktop.