I've tried both the tomcat and jboss bundles, and I get a "lone zero block" error for both while trying to decompress and untar. I've downloaded each of the bundles twice to try to ensure that the files are not corrupt. Posting MD5 hash sums would help.
For alfresco-jboss-0.4.0a, I get:
tar: A lone zero block at 152427
For alfresco-tomcat-0.4.0a, I get:
tar: A lone zero block at 67841
My linux distro is an up to date gentoo 2005.1. My version of tar is "tar (GNU tar) 1.15.1".