2003 is approximately the time of transition from IDE to SATA. Some Dell Dimension mobos had both IDE and SATA controller, so you might check yours. Otherwise... if the hard drive's data connector is a wide, 80-wire ribbon, it's IDE. There might also be a PCI board to enable the use of the SATA connector, but its throughput would be limited a bit by the PCI's max of 100-133 MB/s. That's probably faster than your present IDE drive, but not quite as fast as some of today's fastest spinners running from onboard SATA controller.
The Dell's Technical Specs said primary IDE and secondary IDE. http://support.dell.com/support/edocs/systems/dim8250/specs.htm
Too bad for OP. I didn't recall whether the D8250 had SATA also... the next model out, D8300, has both... I set one up for a guy on his D8300 just last week.