Warning: theological minefield approaching

Here's one that may never be resolved, but to be honest I have never heard the Protestant version of this outside of a history book.
All throughout my checkered Catholic education (ask the MacMan for more background on this issue), the principle information I got about Protestantism is this little thing of justification by faith alone. Now, the way it was presented to me was that Lutherans believed that human nature was so corrupt that any human act is useless, but by the grace of Christ, everyone is redeemed by "accepting Jesus as one's personal Lord and Saviour". It was as if Jesus put a clean tablecloth to cover an ugly creature in order to make it presentable. This is always compared to the Catholic teaching of justification by faith and good works.

Now that my development in Catholic study has matured somewhat since then, I'm assuming that this way of describing justification by faith alone might be a bit...hmm, let's say, simplistic? I'm curious to hear the real belief on this.

Pax.
Iggy