Hey micronator,
for what it's worth, I have a Xoops site. It is running in an ibay, but if it helps, here goes:
1) Setup a Xoops "database" in MySQL;
2) Give a "xoops DB user" enough MySQL permissions for Xoops DB;
3) Install Xoops;
(I have the 3 dirs cache, templates_c, & upload, set at 770 the rest of the dirs are set 750 and all files are 644) This appears to work for me.
When the install is done set the mainfile.php to 444, this is critical.
Also, i use a small php script with all the "secret info", db_name, db_user and db_password, for the mainfile.php. Then move the secret_info file outside of the web root, and point the mainfile.php to the secret_info file. Prevents php from freaking out and leaving all the info readable from the clients browser.
Good luck
Joe