Cannot write files with PHP

[hlstriker]

I'm trying to write a file using PHP but it gives me the following error.

Warning: fopen(/opt/lampp/htdocs/test.txt) [function.fopen]: failed to open stream: Permission denied in /opt/lampp/htdocs/test.php on line 11

Anyone know how I can fix this?

[wmeinhart]

there is no Permission for the User running apache, give write-access for nobody and nogroupe; these are the standardusers for apache.