Outlook Sending Email to Wrong Address

I am using Outlook XP on a Windows 2000 system with SP-3 installed. Some (I don't know how much) of my email is going to addresses not on the email addres list (however, these are people I have recently communicated with via the "reply Command"

I found some patches for Exchange server 5.5 on the MS Web but since they were dated and were indicated for Outlook 98, I assume they were the wrong solution. Help.