permalink issue between two identical servers

i have a php/mysql testing server running on my powermac (unix) and an identical server running on my macbook (intel). identical php5 installs. identical mysql4 installs. identical apache 1.3.33 installs. identical wordpress installs. identical .htaccess and httpd.conf files with same permissions. using custom permalinks works on my powermac, but not on my macbook.

any suggestions?