Installing Concrete5 on one.com
Im useing one.com.
I have been in touch with one.com myself and asked them to switch my account to a PHP 5.2.x instead, but the response was negative.
My advise to you is to switch to another CSM-program that works with one.com or simply change to another host.
This will not help you mayby, but i host a site on ONE.COM and it works fine.
PHP 5.3 and Concrete 5.3.2
But have to turn off all PHP error message, I get some errors. But that can be something else.
Register Globals I have set to off.