MSXML5.dll not a valid Windows image

My PC is running XP Pro with Outlook 2003. Recently, when opening Outlook, I
get error message:
The application or DLL C:\Program Files\Common Files\Microsoft
Shared\OFFICE11\MSXML5.dll is not a valid Windows image. Please check this
against your installation diskette.

The file is listed in the folder with a size of 0. Per another PC, same o/s
and Outlook version, it should be 1393 kb. Can I copy the file from the other
PC? If so, how do I do this? Must I be in safe mode? Can I just drop it into
the directory? Other specific directions?

Also, how does something like this happen? A few weeks ago, this PC booted
into Checkdisk, but when the scan was done, booted normally into Windows with
no error messages. Thanks in advance for your help.