The PGP signatures can be verified using PGP or GPG. First download the KEYS as well as the asc signature file for the relevant distribution. Then verify the signatures using:
$ pgpk -a KEYS $ pgpv apache_1.3.24.tar.gz.asc
$ pgp -ka KEYS $ pgp apache_1.3.24.tar.gz.asc
$ gpg --import KEYS $ gpg --verify apache_1.3.24.tar.gz.asc
Alternatively, you can verify the MD5 signature on the files. A unix program called md5 or md5sum is included in many unix distributions. It is also available as part of GNU Textutils. Windows users can get binary md5 programs from here, here, or here.