I have a HP DC7700 Dual Core connected to a Cisco 3548. The computer keeps loosing and gaining comms every minute or so. If I connect the PC using the same patch lead to a Linksys WRT54G the computer is rock solid reliable.
I have upgraded to the latest Intel driver; upgraded to the latest Cisco Switch firmware; upgraded the BIOS on the HP.
Problem appears on both Vista and XP Pro (same machine just reinstalled.
tried turning portfast off no difference; tried locking speed to 100/full still same problem.