PHP and apache on WIN ME

I have installed the latest Apache server and PHP4, it seems to be running fine, the php scripts execute and do their stuff except that it has problems with file handling. I am testing a guest book and the script produces an error if the data file doesn't exist or can't be opened. I know the script works as I have it running on the web. A similar file handling programme occurs on a free for all links script. What would be causing the problem, I know you chmod file attributes on unix but is there a windows command to do the same as to me (experienced but not expert) it sounds like the data file does not have write access. Many Thanks anyone out there Mark Glendinning