Specs for the HP 5212y Slimline Desktop - Note the 220 watt PSU
Do a Newegg Power Search. For Form Factor, select "Low Profile" and "Low Profile Ready". For Interface, select "PCI Express 2.0 x16" and "PCI Express x16". Further down are options for DVI and D-Sub. Select "1 x DVI" and "1 x D-SUB". However, if one of your monitors has an HDMI input, you can skip this step. Finally, click the Search button.
These are the cards that fit your form-factor and output port requirements. However, many of these cards will require a better than 220 watt PSU. Not sure just how far you can push that power supply, so I won't make any recommendations.
-Wolf sends