That particular file appears to be harmless, it is a part of XP's SP2.
ntio404.sys - File Information
Could you run a scan with hijackthis (if you can)? and post the log file?
http://www.hijackthis.de/downloads/HJTInstall.exe
If it completes, the log file output
should be able to give us all the necessary information to help you fix the problem.