To install these additional clip art files so that you can 
access them from the Microsoft ClipArt Gallery, follow
the instructions below:

1.  OPTIONAL.  Copy the .pcs and the .cag files from the
Clipart directory on the CD to their
final destination, for example, your hard disk.  You
may elect to leave them on the CD if you wish.
2.  Launch PowerPoint
3.  From the Insert Menu, select Clip Art
4.  If this is the first time you've run the
ClipArt Gallery, you may get a message telling
you that there are new packages to add to the ClipArt
Gallery.  If you get this message, click the Add All button
and ClipArt Gallery will proceed to add those new pictures.  
5.  Now, in ClipArt Gallery, click the Organize button.
6.  Choose Add Pictures
7.  Browse to the location in which you placed the .pcs
and .cag files in Step 1.
8.  Select the .cag file you want to add, or hold the CTRL key
while clicking to select multiple .cag files
9.  Click Open.

The new clip art pictures will be added to the ClipArt Gallery.