Is Soft4Download, Inc. a legitimate business, what liabilities do I
run into by buying software from softw4download.com?

There's some useful info here:

http://www.tek-tips.com/viewthread.cfm?qid=1004567&page=1

The company is legitimate.  I've bought software from them before. 
But be aware.... the software is not even OEM.  OEM is short for
Original Equipment Manufactaurer...meaning it comes with a piece of
hardware.  In the case of most MS Office software and Operating
Systems, it usually comes with a new PC.  Microsoft offers very little
in the way of support to OEM purchasers, but you DO get a certificate
of Authenticity and sometimes a manual.  You also can get the disk
replaced if necessary by providing the Key Code.  The software from
Soft4Download is genuine, but it isn' really OEM.  It's actually
developer software which is given free to developers.  NOT so they
will have free software... but so they can make THEIR software
compatible.  I've had custoamers bring their computers to me with
developer copies of WIndows XP installed and want me to get updates. 
Can't be done.  Developer software is never intended to face the
internet and require updates.  Microsoft provides the updates to
legitimate developers through specific servers for that purpose.

The software from dthis company is cheap because Microsoft gets no
royalties for its deployment.  I hope this helps