Managing Problems with the AUTOEXEC.NT File
You may encounter a message, particularly after the Windows XP SP2 upgrade, about either CONFIG.NT or AUTOEXEC.NT being "...not suitable for running MS-DOS and Microsoft Windows applications." It's possible the DOS 16-bit COMMAND.COM program and/or one of those files has become corrupted if you get this message. There is another possibility as well; described below.
Microsoft has a knowledgebase article on this. What it basically says is that you need to replace the files AUTOEXEC.NT, CONFIG.NT, and COMMAND.COM which are found in your Windows System32 folder with the same-named files found on your original OEM Windows XP CD-ROM.
In addition to the CD-ROM, copies can also usually be found in the \Windows\Repair subdirectory so you don't need to panic if your XP CD disc is not handy.
The replacement should be a one-time fix; however, some versions of the Windows XP SP2 update have code that will automatically delete the AUTOEXEC.NT file if found in the System32 folder on the theory that all software should be 32-bit and not 16-bit. But, you might still want or need to run older programs and will need the AUTOEXEC.NT file to do that.
If this happens to you try copying the AUTOEXEC.NT file to the System32 folder under the Windows folder and then right click on it, select Properties, and check the Read Only attribute. This should work.
If it does not you will have to re-copy the file to the proper directory after every restart of the computer. While a PITA, you can automate the process using a batch file with a little work.
First, make a copy of the AUTOEXEC.NT file in a directory of its own on the C: drive (I'll assume it's in C:\PITA\AUTOEXEC.NT for this example). Make the file read only (right click on it, select properties, check the read-only box).
Now open a text editor (Notepad will do) and type the following lines...
@Echo OFF Copy C:\PITA\AUTOEXEC.NT C:\Windows\System32\ Attrib +R C:\Windows\System32\AUTOEXEC.NT
Save this file as C:\PITA\DOIT.BAT. Then, open an Explorer window and navigate the the C:\PITA folder so you can see the DOIT.BAT file. Right click on the file and drag it to your desktop and release. When asked, select the Make a Shortcut Here option.
Then, after each restart all you have to do is click on the DOIT.BAT shortcut and the file will be copied to the right place and marked read only automatically. (You should also be able to put a shortcut to DOIT.BAT into your Programs|StartUp folder and have it run automatically if you don't want to have to remember to click on an icon.)
Note: Some versions of Windows XP call the Windows folder WINNT. If you have one of those, substitute WINNT for Windows in the above.