Please note that Mechwarrior 4: Mercenaries is NO LONGER offered by Microsoft, or any other entity, for free legally. We know of at least one company offering a download link, to the best of the staff's knowledge the company does not have the rights to distribute MW4: Mercs freely (or to charge for it honestly).
As such, ANY links to download Mechwarrior 4: Mercenaries (or any other copyrighted game) will be taken down and warnings issued.
If there are any questions please PM a Moderator, we will gladly answer them.
Bosefius