I checked if in php.ini the instruction extension=php_mysql.dll is uncommented and it is, also the extensions directory setting is ok and the file exists.
The miniserver I previously used has php5 in it and XOOPS worked.
What else should I verify?
thanks again
cristina

I have tested XOOPS on sourceforge uniserver and had no troubles, now that I have to run it on a windows 2003 server with apache2, php5 and mysql5 (the version on uniserver was 4.x.x) I get the following message:

This page cannot be displayed due to an internal error.

If you are the administrator of this site, please visit the XOOPS Troubleshooting Page for assistance.

Helpful infomation you should provide while asking for assistance:

Error [Xoops]: MySQL extension not loaded in file C:\Programmi\Apache Group\Apache2\htdocs\class\database\mysqldatabase.php line 74

Thanks for any help
cristina