You may have run into the same problem I just did when installing XOOPS 2.0.6 on someone's server that looked to be perfectly set for Xoops. It had PHP, MySQL, etc. - everything set properly.

However, he set the file permissions on mainfile.php, and the three directories to 666. Everything came up fine during the installation, but he got a blank screen.

So, when I installed it (I watched him the first time) I chmod'ed to 777 instead of 666 - and we did everything the same. This time, it worked like a dream.

Just a general FYI...