To restore grub, use the PCLinuxos live cd and run the mbr repair tool. This will re-install grub, and restore your Linux installs.
Will all the original files and set up stay they same? My dual XP install got corrupted about 2 years ago. Obviously I have gotten along fine without it but I always wondered if I could fix it and still keep my Linux install just the way it is. I wasn't keen to just try.
If you have an XP installation disk you can either do an automatic repair of the existing system, which is really a reinstall of all the original files without reformatting the partition, or a complete reinstallation with formatting, and neither should bother your Linux installation, beyond rewriting the MBR code.
If you have a computer mfg's recovery disk that re images the hard drive to be as it was when purchased, it will wipe the Linux installation, including partitions, from the drive.