(From a recent mailing of Kyösti Mälkki)

Read i2c/README.bitmb.
Your /proc/pci or lspci must show VT82C586B (note the last B)
to make it work. This is an upgraded version of VT82C586/A with USB and
ACPI support. The i2c-lines are accessed through the ACPI part.

This is my PCI bus data:

00:07.3 Bridge: VIA Technologies, Inc. VT82C586B ACPI (rev 10)
        Flags: medium devsel

South bridge VT82C586B is in these chipsets: MVP3, VP3, VP2/97, VPX/97

I don't see the last two PCI devices if USB is not enabled in BIOS setup.
BTW, my motherboard is FIC VA-503+.

Hope this helps for now, I will write better documentation some day.