This probably comes too late (3 months?), but Dell computers (many, anyway) allow you to disable HT in the BIOS. Although the non-HT boxes may be slightly cheaper than the HT's, when you figure your time to boxthe returns backup, re-build the order for non HT's, perform return return, wait for replacements to arrive, receive replacements, set up, etc., you will probably save money just keeping the HT boxes and disabling HT.
Also, unless there is a known bug in HT implementation, the problem is just as likely with the Windows code itself - like a timing problem(s) with block/resume processing that the code 'gets away with' on slower or non-HT processors (since only 1 thread can be running at a time in non-HT, the 'contention' is removed by definition, and the problem situation is therefore either 'impossible', or at least extremely rare).
Hopefully, if this is actually aWindows code problem, it will one day be corrected and you can then just turn HT back on??