I just found a, significant at least to me, bug with the latest TCPOptimizer in WinXP. If you install a PCIe network card in a system as a secondary connection, then run TCPOptimizer, select Modify All Network Adapters, then Optimal, it completely breaks the PCIe network card in Windows.
It renders the card 'unable to start'. This is obviously an unusual situation and in an old OS but it might be worth others knowing about.

Don't use Modify All Network Cards if one of them is a secondary PCIe card.