BlindWolf,

Can you find out what versions of each package you have?
Plesk -
Apache -
Linux (if that's what you're using)
PHP -

I really don't think it's a Plesk issue, but I could be wrong. I'm not quite sure what Plesk has to do with resolving paths... to me it sounds more like a php.ini / vhost.conf issue. The thing about Plesk is, it's really just a user interface. I've used Plesk and cPanel, as well as media temple's admin area, and they all pretty much do the same thing - you can administer domains, DNS, files, databases, etc. But when it comes down to the functionality of your scripts, they all behave the same way no matter what your control panel environment (at least, in my experience). The key factors are your Apache/PHP/MySQL versions and how they have been configured/installed.

If you're using PHP 4, I'd recommend upgrading to 5. Usually upgrading to the latest stable version of anything will solve a lot of issues that are harder to figure out, such as this one. Like I said, I've installed Drupal - on Plesk installs as well as GoDaddy's "one-click" setup) and never had an issue where something didn't install because it couldn't resolve a path. The problem in my eyes is most likely deeper than what control panel you're using.