This is just a documentation of my experience. Maybe one day someone interested might see what caused all this. I am not the only member here to experience some or all of these errors.

First there was the old:
Check that certain classes haven't been defined by PHP plugins Your version of PHP has defined some classes that conflict with SilverStripe's. The following classes are at fault: HTTPResponse

Fixed this by renaming all instances to something else like; SSHTTPResponse

Second was:
Warning: fopen(/tmp/silverstripe-cache-home-thesite-public_html/manifestClassParse-_home_thesite_public_html_cms_code_AssetAdmin.php) [function.fopen]: failed to open stream: Permission denied in /home/thesite/public_html/sapphire/core/ManifestBuilder.php on line 398

Fix this by manually creating directory; "silverstripe-cache"

After all that I have:
[Warning] HttpRequest::__construct() expects at most 3 parameters, 5 given
GET /?flush=1
Line 112 in /home/thesite/public_html/sapphire/core/control/Director.php

Still no joy with the SS installers

Thank you willr. I have re-installed SS so many times that I just gave up in the end. Now I've already installed Drupal(very easy) and started customization. I will try SS again one day maybe. Thanks for the help.

Please read some of the comments here to see what others think of SS:

http://php.opensourcecms.com/scripts/details.php?scriptid=61&name=SilverStripe