I must say, very well done, tried it out on my machine, an HP EX470, and it worked no problems! Though I might recommend a slight modification to your patch. Instead of replacing "0x0965" with "0x0968" you could add an extra line so that it doesn't cripple the driver for systems that use the 965 Southbridge:

static int __devinit sis190_get_mac_addr_from_apc(struct pci_dev * pci_dev, struct net_device *net_dev)
{
        struct pci_dev *isa_bridge = NULL;
        struct sis190_private * sis_priv = net_dev->priv;
        u8 reg, temp;
        int i;

        printk(KERN_INFO "%s: Read MAC address from APC\n", net_dev->name);
        
        isa_bridge = pci_find_device(0x1039, 0x0965, isa_bridge);
        if (!isa_bridge)
                isa_bridge = pci_find_device(0x1039, 0x0968, isa_bridge);
        if (!isa_bridge) {
                printk("%s: Can not find ISA bridge\n", net_dev->name);
                return 0;
        }