I know the above is an old post, but I had this problem today and found this post in Google.
So for others with the same issue:
I had the same problem. I installed Entropy, then afterwards the Personal Web Sharing service (aka Apache server) refused to start because of a "Bus Error".
It's because Entropy tried installing PHP 5 when I had already tried installing PHP 4 myself. The solution for me was:
Open the /private/etc/httpd/httpd.conf file and remove all lines with references to PHP4.
Restart apache (at the terminal: "sudo httpd restart")
The bus error then disappears and Personal Web Sharing starts with no problems.