Well, Im not saying that SNAC is definitely the issue in my school. As I said, the Ethernet/Fibre converter in our cab2 doesn't seem to be getting a solid link so it could well be that at fault. But we certainly do have fibre that is shared which is logically partitioned on the switches.
Anyone that has a legacy network that uses those c2k routers will have an IP address and subnet settings set by them so therefore that legacy network could be affected by anything c2k/northgate/HP do. Paul and myself both got these issues when SNAC was turned on, so I guess its human nature to think the two are connected. I'll let you know what happens here anyway, whenever (if at all) the issue is solved.