If it's got an AGP slot, it must be one of the motherboards designed to enable you to upgrade the graphics.
I would suggest you get a reasonable, but not over the top card, otherwise the processor will be limiting performance anyway. Such as a GeF4 MX440 card, with 64Mb RAM.
If you look in the BIOS and/or the manual, it will should tell you what to do (if anything) to disable the on-board graphics.
It will also pay you to get the latest intel 810 chipset drivers from the intel site.