KT133a/166 FSB questions..

On the KT133A chipset @166FSB are the PCI/AGP buses o/c'd as well or is there another divider after 133? The reason I am asking, is I am hitting 166 on a kk266-r and everything is working great except when I try to get online my modem craps out. I just found it odd that the Radeon seems as happy as can be when the FSB is at 166, because I read somewhere that is doesn't like higher bus speeds. Also would a USB or Serial modem avoid this? At 150 the modem starts to work again, which is where I am at now.