Today I've tried to setup PHP with MySQL but for somehow the Apache crashed, when trying to query something. Funnily the SHOW command worked fine, ie: SHOW DATABASES;. The module was loaded correctly and appeared in the phpinfo(). So I've double checked all config and log files but nothing happened or gave me a clue. Browsing the php.install newsgroup also didn't gave me any idea what could it be - but - then I've remembered that I've downloaded the 5.1.22-rc-community release, instead of the 5.0.x release. Downgrading to 5.0.45-community-nt luckily solved the mysqli connector problem and everythings seems to work fine now.

Hope this might save someone's time.