I have kind of the same problem. I'm running XAMPP 1.6.6 (Apache 2.2.8, PHP 5.2.5 and MySql 5.0.51) on Vista Ultimate and the Silverstripe version is 2.2.1.
I've checked that I have full permissions to my Silverstripe-directory and all the files in it.
Still the install screen complains:
Unable to detect whether I can write to files. Please ensure C:/xampp/htdocs/ss1/.htaccess is writable.
And the same with "C:/xampp/htdocs/ss1/mysite", "C:/xampp/htdocs/ss1/tutorial" and "C:/xampp/htdocs/ss1/assets".
I've enabled mod_rewrite in Apache and it gives this error message when trying to install:
# ERROR: mod_rewrite not working, redirecting to mod_rewrite test page
I will now try and direct you to rewritetest to troubleshoot mod_rewrite
After that it loads the rewritetest.php but doesn't output anything.