1. Make sure you have SAFEBOOT unchecked in Start \ Run \ type: MSConfig \ check; Boot.ini... If I understand correctly this is what you mean in your message but in case of a doubt, check the
image here or
here.
2. Do a online
Virus Scan
3. Delete user and system temp files (Start\Run\type: %temp% and temp in Start\Run) also delete Internet temp files from the Control Panel \ Internet Options.
4. Disable Startup programs in Start \ Run \ type: msconfig \ startup tab \ uncheck all but the antivirus process.
5. Scan the msconfig.exe file with
this online malware scanner (msconfig.exe location is C:\WINDOWS\PCHEALTH\HELPCTR\Binaries\). If you have to (if infected), delete msconfig.exe you can always replace it with a fresh copy from the XP CD or download a copy... it doesn't need to be installed.