Question : Problem: how can I run four monitors on HP Pavilion Elite m9400t?

I would like to run four monitors on my HP pavilion elite m9400t desktop.  I currently have an Nvidia GeForce 9500GS PCI video card (not PCI express).  this card has three ports:  VGA, DVI, HDMI.  Each of the monitors  has VGA connections, so I used the VGA input for one monitor and the DVI slot (with VGA<->DVI converter) for the second monitor.

The HP Pavilion elite desktop has 1 more PCI slot (aside from the one used by the GeForce 9500gs) and 2 puny-looking PCI express slots.

What do i need to do to get to 3 and 4 monitors?  

Answer : Problem: how can I run four monitors on HP Pavilion Elite m9400t?

seeing they will be running on two separate interfaces, you're more likely to be free from running into any issues than if you were to use 2 PCI cards, i'd say.  although, I would stick with the same brand - so if I were you, i'd go with a similar nVidia card.  

i suppose if you wanted a "for sure" answer on whether the video card you have now and the one you are looking to purchase are compatible, you would need to do some research on the card you're looking to buy, perhaps calling the company to verify.