As far as I remember, Inkscape 0.46 does not have built-in support for unicinvertor, so unless you have installed it yourself, it probably won't work. On a Windows system you can find out for sure by viewing the file C:\Documents and Settings\username\Application Data\Inkscape\extensions-errors.log In my case I get the message :
Extension "Corel DRAW Input" failed to load because a dependency was not met. Dependency: type: executable location: path string: uniconv
Alternatively, when you try to load a file you should see an entry for CorelDraw 7-X4 .cdr files in the file-types box. If this is not there, then you have two options: you can install uniconvertor yourself from the website http://sk1project.org/modules.php?name=Products&product=uniconvertor or you could try a newer development version of Inkscape, which would include it as part of the package. This depends on which OS you are running. Uniconv is a python package so if you install it yourself, you may have to install Python first.
I can confirm that on a recent Win32 development build I was able to load some of the .cdr files from the website you referred to.
hth Alvin