I experienced some system weirdness (though not as extreme as you have) with my ASUS P4PE board with HT enabled... it turned out that my firewall, LNS 2.04, didn't work well with HT enabled (the LNSFW1 driver).
If your system works normally with HT disabled, try using a different FW as a test... Sygate 5 works very well for me with HT enabled.
If you have a NIC installed, try using the on-board mobo NIC.
I suspect that what you see is some serious conflict with your FW driver(s) and your system drivers competing for the same system resources.