404s after install

First of all, my server is running on:
PHP version 4.3.6
MySQL version 4.0.18-standard
Apache version 1.3.29 (Unix)
The installation goes fine – tables are created fine, random password is generated, i can log in as ‘admin’ with the password. First thing I do is change my password in ‘My Profile.’
However, right after I change my profile and press “Submit,” all goes to hell and everything shows up as 404. My FTP shows the files still uploaded in their folders, so I’m wondering if it’s because I didn’t CHMOD a file or folder properly.
So now I’m wondering what I need to do to get my install working properly. If someone needs more info to help diagnose I’ll respond as soon as possible.
Thanks