No. There are three types of graphic cards available on the market these days: PCI, PCI-E, and AGP. These all correspond to matching graphic card slots on your motherboard. I believe the Dell GX280 has a PCI-E graphics card slot (you'll want to make sure).
The other thing you need to determine is the form factor of your PC. I believe the GX280 came in three difference design styles: Small Mini-Tower, Small Desktop and Small Form Factor. Of these, only the Small Mini-Tower design will accept a full sized graphics card. The other two require low-profile or half height graphic cards.
Additionally, what graphics card you can place into a Dell GX280 depends on what power supply you have installed. Higher powered graphic cards will not work with a low powered power supply installed. Replacing the power supply will also depend on what design style GX280 you have.