BMP files won't work...

I've just been trying to get a downloaded campaign to work, and mission 1 won't load because it can't find an anti aircraft gun in the library.
Its there, but I've realised that it and about half of the BMP files in various Textures folders are not displaying... ie coming up when I manually open them as:
"picture failed"
I think I know why this is, either:
(i) the download was corrupt, or more likely,
(ii) I recently mistakenly removed some utility programs from Windows XP....'Paint' is the only one I'm sure about, and I can't get 'em back from just exploring and picking individual programs on the original XP disc.
Question is: can I simply download an image opening program to view the BMP files properly if so, what, or..... (curses) am I stuck with reinstalling XP from scratch?
Its there, but I've realised that it and about half of the BMP files in various Textures folders are not displaying... ie coming up when I manually open them as:
"picture failed"
I think I know why this is, either:
(i) the download was corrupt, or more likely,
(ii) I recently mistakenly removed some utility programs from Windows XP....'Paint' is the only one I'm sure about, and I can't get 'em back from just exploring and picking individual programs on the original XP disc.
Question is: can I simply download an image opening program to view the BMP files properly if so, what, or..... (curses) am I stuck with reinstalling XP from scratch?