You borrow a good xp disk. Read up on how to do a "repair". Fairly simple but you may loose some updates and maybe have to reload software.
Use windows or linux live cd to replace that file.
I love to use live cd's. They are easy to use and easy in most cases to make or get. They can be used to copy over the entire disk or just files you want. Some windows based can perform Ntbackup to save your install.
You can save data off to network or cd/dvd's or flash or usb drives. Even online storage if you have it. Free places offer online too .
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10