It's possible, just install to 2 different directories.
I.E.
C:\Program Files\Blockland andC:\Program Files\Blockland2 or something.
Why you want to do this, I'm not sure, but that's how you do it.
If you're on MS Vista be sure to use Ladios's easy running on Vista trick on both folders or have both games installed to a "master" folder.
IE
C:\Program Files\Blocklands\Blockland1, 2, 3, ect...