Definition of .htaccess leads to an Error 500

Hello,
I use WordPress 2.9.2. My problem is that when I set permalinks wordpress tells me that it does not have access to the .htaccess file (even I temporally give full access to this file). So I copy/paste the .htaccess contents suggested by wordpress to a created .htaccess file (created by “touch .htaccess”). Afterwards, when I try to go to the homepage or go back to wordpress administration I get an Error 500. In case I delete the .htaccess file, and define the Custom permalink strucuture by writing an “index.php” in front of link structure(/%category%/…”), it works. However, I do not know if search machines will have a problem with this type of link structure. In addition I want to know why the definition of a .htaccess file does not work for me .
Maybe obne of you has an idea

Thx.