I've managed to sort it out. FYI, I did follow the tutorial.
However, instead of using the installed MySQL, ie. ver. 4.XX, I installed MySQL server and MySQL-Max 5.0.22, as well as a newer version of PHP. The errors that I posted was apparently due to some missing header, though I did not know whether its MySQL or PHP.
Once I managed to start Apache2 without any errors, and able to view MySQL info in phpinfo page, the ISPConfig installation works like clockwork without any errors.
Currently, I am trying to find out how or where ISPConfig keep the templates for creating the VirtualHost for vhost_ispconfig.conf, as I need to modify it to add some cronolog and awstats, as well as skel for domains added using ISPConfig.
Any ideas? BTW, thanks for replying to my post.