If you installed "KDE" during your Mandrake installation, you can use Konqueror
as a helper application (it has support for pdf files).
Go to "Edit" then "Preferences"
Under "Category" find "Helper Applications" Click on "New Type..."
Enter this information:
MIME Type: application/pdf
Description: Adobe Acrobat
When you see the option "When a file of this type is encountered"
click on "Open it with" type in "konqueror" (without the quotes).
Put a check mark on "Always ask me before handling files of this type".
You can uncheck this after everything is working.
You can do the samething with any other program you want Mozilla to use.
For more plugin options checkout the Mozilla Plugin Support