Well, as far as I know, the i845GL series does not have AGP support.
*support.intel.com/support/graphics/intel845g/sb/CS-009073.htm
The main advantage AGP cards have over PCI cards is their amount of bandwidth and the ability to offload a major chunk of graphics processing at fast rates to the GPU. Remember that you will get literally very little performance boosts in even pre-2003 games at the lowest possible graphics settings with a PCI card. If you're a gamer, consider upgrading to a motherboard that supports AGP8x/PCIe rather than wasting money on a PCI based video card. I remember seeing a PCI based GF2 MX card for around 2.5k and DKant was telling me about a Radeon 92xx card for around 4.5k. Dont even think of spending that money on a PCI card that wont even get you half as much performance than a cheaper priced FX5200.