http://www.visualtour.com/downloads/xp_fix.exeYou didn't go wrong this is a very common problem
There are alot of possibilities like disk cleanup utilities that mistake autoexec.nt and config.nt as backups to the older versions of windows autoexec.bat and config.sys
All this program does is replace 3 missing or corrupted files
command.com, autoexec.nt and config.nt
It should be a permanent fix unless you have a program running at start up that is corruptiing the files