You should run HWinfo32 utility program to confirm if any upgrades have been added to the system:
HWiNFO32
Dell OptiPlex GX260
Probably has: 2.26 GHz P4 CPU, 256MB RAM and 20 GB HDD.
Dell 2X378 Optiplex Motherboard Features:
* Audio ADI 1981A Audio Controller - Line In, Line Out, and Microphone
* Video Integrated AGP Graphics Video VGA Connector plus AGP 4x/2x AGP Slot
* Four (4) Back-Panel 2.0 USB Ports and Two (2) Front-Panel
* One (1) Serial Port
* One (1) Parallel Port
* One (1) 4x AGP Slot
* One (1) 10/100 Ethernet Network Port
* Two (2) Parallel ATA IDE Interfaces with UDMA 33, ATA-66/100 Support
* One (1) Floppy Diskette Drive Interface
* PS/2 Keyboard and PS2 Mouse Ports
* Expansion: Two (2) PCI Slots and One (1) 2X or 4X AGP Slot
Dell GX260 User Guide here