I need software for recording live sound (usually voice only) from a
line level into my notebook computer.  I usually get a good line level
from either a mixing board or a wireless microphone receiver.  I have
Sound Forge 7 which records fine.  The problem is that I need to be
able to have a limiter for high volume levels.  I usually record
speeches and sometimes the speaker gets loud.  If I set the record
volume low enough so that it doesn't peak, the overall volume of the
recording is too low and it is too close to the noise floor.  If a
digital recording peaks, the sound terribly distorts unlike an analog
recording so it is critical that the input signal be limited so that
it does not go past 0db.

Usually this is done with outboard equipment, a separate limiter box
that will automatically lower or limit the signal when it reaches a
certain point.  Sound Forge will limit volume but only after it is
recorded.  The problem with this is that once it is recorded and it is
too loud, it is distorted.  I need a software solution that will limit
the volume before it is recorded so that it will not distort.

Is there any program, plug-in or software that does real time hard
limiting of a line level input signal during recording?

I'm a computer programmer and live sound engineer.

The problem you've got is overloading the AD converter. So when the AD
converter see's a signal that's too loud, digital clipping occurs and
that gives the distortion.

I don't think you're going to find any software that will fix this
*because*, the software kicks in *after* the AD converter. Ie, damage
is already done.

For your instance the best solution would be a computer that had a
built-in compressor/limiter that was before the AD part, and have
software control the compressor/limiter.

I don't believe you'll find a computer like that. 

Because you're looking for software as a solution, and I don't think
there is any, i'll offer a hardware solution that you already know of
- hopefully not offending google researchers.

http://www.musiciansbuy.com/Behringer_COM800_MiniCom_COM800.html

This, or other cheap compressors made by Behringer should do the trick for you.