If this was a Physical Machine one would boot it with the Windows XP Install CDROM to the Recovery Console and replace the file via the Command Line, so I'd do the same with a Virtual Machine.  This would probably be the safest way however error messages are not always accurate in that while one may be told a given file is corrupt it may not actually be corrupt.  For the sake of argument though lets assume it is corrupt, what I do is rename the file <filename>.bad and copy the good file from the install disc to the proper location.  Then try running the Virtual Machine.  If all is well then the file was then in all likelihood corrupt however why was the file corrupt, was it due to a bad spot on the Host's physical hard drive, corruption in the file(s) that composes the virtual hard drive or corruption in the filesystem on the virtual hard?  This is important and tests should probably be done after first backing up the Virtual Machine or at a minimum any User Data that is stored in the Virtual Machine out of the Virtual Machine and off of the physical disk.

There are other ways to access the virtual hard disk.  Like using VMware Fusion's VMDKMounter (which was removed in VMware Fusion 4) and NTFS-3G however as previously mentioned booting from the install disc is the safest.