permission to write to text file

Hi, I just installed PHP on IIS 5, Win XP, and I keep getting permission problem to fwrite, fopen and fclose the txt file. I have set the permission to read, write, execute by doing this: I went to administration tool ->IIS -> go to default website ->select my virtual directory -> find the txt file in my directory -> properties -> pick the file tab and check read, write and script source access. I did the same thing for the php file. I also tried doing the same thing to the whole site folder. None works. Is there anything else I should do? Or is there something wrong with my setting/installation? Any help appreciated. Thanks, rene