Will your Intel CPU run EM64T
 

If you check the latest Intel® Pentium® 4 Processor on 90 nm Process Specification Update (i.e. the errata list) you will see that there are a lot of new errata in E0 stepping.
There is also a very nice table with S-Specs for CPUs where you can find out which cores support EM64T and which don't.

For example I have product code ending in SL7J5 and it doesn't support EM64T. As the matter of fact, no unit below 3.2 GHz does.

http://www.theinquirer.net/?article=20852