Was there nothing on your existing GPU?
Also, are you certain that your slot is PCI-E?
Card name: Intel(R) 82945G Express Chipset Family
Manufacturer: Intel Corporation
Chip type: Intel(R) 82945G Express Chipset Family
DAC type: Internal
Device Key: Enum\PCI\VEN_8086&DEV_2772&SUBSYS_5050107B&REV_02
Display Memory: 128.0 MB
Current Mode: 1024 x 768 (32 bit) (75Hz)
Specs said it had one PCI-e x1 slot, two conventional PCI slots, and one PCI-Express x16 slot.