Warning! – Failed to move file (Joomla 1.0.x, Joomla 1.5.x) when trying to install some components in a freshly installed joomla 1.5 Version site.
Solution to this is either to change permissions to 777 for tmp directory OR enable the legacy mode
To locate the tmp directory
(Login to Admin Area) > Global Configuration > Server > Server Settings >Path to Temp-folder