If you have XP you should be able to do a "system restore" back to a point before your installation. Have you tried that?
I've fallen foul of the new Microsoft Download system. I inadvertantly downloaded the new update files "Windows XP KB842773" and "software distribution service 2.0"
I now find that I cannot install programmes which ran previous to the above event. Error message reads "C:\WINDOWS\SYSTEM32\AUTOEXEC.NT. The file is not suitable for running MS-DOS and MICROSOFT WINDOWS applications"
How can I reverse the effects of this download?