Yes, but not the best way to do it.
Go to PDF Exports presets and pick Press. Click on the advanced tab and select CMYK under color. Make sure that "include ICC profiles" is not checked so as to bring in a rgb profile. You are not guaranteed the best result by doing this.
The best way is to open the Links window, click on an image and select Edit Original from the flyout meny of the triangle at top of window. The image should open in Photoshop or Illustrator (or another image app) and you can change to cmyk. Then, in links window, pick Update link. This will give you the proper result and should not take more than a few minutes for 25 images.
Using OSX 10.3.9 on a G4