I just had this same problem and was reading this forum to try and find an answer (though sadly i did not). Instead i decided to boot from my original windows install disk and run the recovery console (press R). at this screen type 'FIXBOOT', it will prompt you for a confirmation so just say yes (type 'y'). It will write over your previous boot files BUT NOT YOUR PERSONAL DATA!!!!! after this runs and says that it has completed successfully, type 'exit' and the console should quit and your computer is back.
edit: caution, i think this is only a temporary fix (meaning you'll have to go through the same procedure every time you boot your computer) so i would recommend backing up all of your files onto an external hd and then reformatting your computer (by the way i have the same computer, Dell Inspiron 5100, so this fix will probably work the same for you as well).
Was having the same problem. Followed the instructions, but computer still won't boot. Now, its not even giving me the option to boot from CD. The new message Reads "Windows XP could not start because the following file is missing or corrupt:\WINDOWS\SYSTEM32\CONFIG\SYSTEM"
At this point, I just want to do a clean reinstall of XP. There is no data of importance on the computer.
Any help would be greatly appreciated.