it seems the problem is caused by something unusual on your machine. Symantec software would be the first choice, isn’t it configured differently than on the other machines you tried? Some kind of on-line scanning or checks. I believe I tried MEW on the machine with Outlook 2002 and Office XP and there was no problem.
Could you send me the info about your machine configuration? Run msinfo32 utility, File | Save. Ideally from both problem and non-problem machine to compare. It can be any small tool you installed long time before and forgot about it.