Can't Install Joomla 1.5

Yes I'm the newest of the newbies...
I installed SohoLauncher (so know I can do that) and thought better of it, uninstalled it and now trying to install Joomla 1.5 instead.
It will not install. It says there is already a file in the main directory of my domain (and tells me to delete it)
But I also read from hostpapa not to delete the original files that came with the setup (which is all I should have now)
Why are there tutorial to install every content management system except Joomla in the Video Tutorials?
Any one can shed some light it's much appreciated
Sorry to be do dumb!