I'm trying to install a Geforce 9400 GT card but I heard that I have to disable integrated graphics for it to be detected. There's no option in my BIOS that's even remotely related to graphics, (STI, P/S2 mouse, whatever) and the only thing related to integrated or onboard I could find was audio. I've already uninstalled the drivers and restarted numerous times with the monitor connected to the new card but it still won't detect. Any other way that I could disable integrated graphics? I'm using HP Pavillion, AMD X4 9550 with Geforce 9100 graphics if that helps.

You said...
HP Pavillion, AMD X4 9550 with Geforce 9100

I assume you have opened the case and can see the MB?

What I would do is this...
Get the model # of your motherboard, and google for a owner's manual for it.

Why?
There may be a jumper setting on the main board to disable the onboard graphics and enable the graphics card slot.

If this is your computer - HP Pavilion A6720F
or this - - - - - - - - - - - - HP Pavilion Elite m9517c
Then this may be your motherboard - Asus HP Viola GL8E M2N78-LA
OR this may be - * Motherboard manufacturer's name: Pegatron M2N78-LA
* HP/Compaq name: Violet-GL8E

And HP offers documentation. For the latter...

But I have not found jumper settings for you... :-/
Sorry about that... may be a dead end.