I've burned the ubuntu server installer .iso to a CD. When I try to boot from it it tells me the disk boot failure message. I know it's not the CD drive that's the problem because I get the same error on multiple computers. Is there anything I have to do besides burn the .iso to the CD to make it bootable?

Burning the iso is all you should need to do.
Sounds like the iso was corrupted in some way. The ubuntu download sites usually provide an md5 checksum for all downloadable files.
After downloading a file, it's usually best to create an md5 checksum. This checksum should match the checksum provided by ubuntu. If it does not match, then the file is most likely corrupted.

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