Installing on CentOS 6 with Apache 2.2.15
If you are sure that mod_rewrite is enabled and working you could try to get past the system requirements check if you change the url during the step "Verify requirements" like this:

Standard URL like this:    
core/install.php?langcode=de&amp;profile=standard
change it to:
core/install.php?langcode=de&amp;profile=standard&amp;rewrite=ok


You add 


  &amp;rewrite=ok


to the url. This will normally be done through .htaccess. Then reload the page or click try again and you should get past this warning.

But it seems that something is not working as expected with your mod_rewrite, so you might encounter trouble later on.