If you have XP Service Pack 2 running on AMD Athlon-64, and have Norton Cleansweep's Smart Sweep and getting one of these "Error":
Explorer.exe application Error
or a 0xc00000005 Stop error
Review this MS Article
http://support.microsoft.com/default.aspx?kbid=873155
My personal suggestion would be to
not have Cleansweep at startup. But rather bring it up yourself before you install a new application.
Also, do not remove the Data Execution Prevention feature of SP2 (as the MS article suggests). Doing that will make your Windows more open to malware and viruses.