This is not a get rich quick scheme but many people have made good money mining bitcoins.  What is a bitcoin you ask?  Bitcoin is a peer-to-peer currency. Peer-to-peer means that no central authority issues new money or tracks transactions. These tasks are managed collectively by the network.  New coins are generated by a network node each time it finds the solution to a difficult mathematical problem.  There will be a maximum of 21,000,000 generated bitcoins and because of this limit, bitcoins are divisible to 8 decimal places.  In other words you can send fractions of bitcoins to people.  Like many currencies the value fluctuates.  As of this blog entry its between $13 and $14 USD.

As of July 2011, there are just over 6.8 million bitcoins in existence.  New coins are slowly "mined" into existence by running a program that searches tirelessly for a solution to a very difficult math problem. When a solution is found, the user may tell everyone of the existence of this new found solution, along with other information, packaged together in what is called a "block".  Blocks contain 50 bitcoins at present. This amount is an incentive for people to perform the computation work required for block generation. Roughly every 4 years, the number of bitcoins that can be "mined" in a block reduces by 50%.  In other words, while the bounty is still 50 bitcoins, hop on this gravy train!

You have two options when it comes to mining for bitcoins.  If you have a good video card, you can try going solo and crunch numbers for weeks or months for a big payout. Or, if you prefer a steady payout, you can join a mining pool and equally share the bounty for your share of work put into it.  If you have a slower video card, a mining pool will be the only way you can stand a chance at finding the blocks before someone else does.

The better the hardware, the better the hash rates you'll get.  ATI is taking the crown here.  Here's how my systems fare at my house.

My hubby and I have quad core 860's with 5870's getting 346 Mhash/s
Our kids dual core with a 5570 is 67Mhash/s
Our myth tv pvr front-end with a 4650 gets 21.6Mhash/s 
Lastly my dual core laptop with a GeForce M230 gets 8 Mhash/s (I don't bother mining with this one)

The higher the hash rate, the more my video card contributes to solving the mathematical problem and thus giving me more of the reward.  Overclocking can increase those numbers but it will also increase the heat generated and the electricity needed to power the system.  The next hurdle is seeing if this is worth jacking up your electric bill.  With those systems in place I can get a bitcoin every 4 days.  With a bitcoin value at $14 I can make $105 a month doing this.  How much of that will get sucked up by a higher electric bill is to be determined.  For those who leave their systems on 24/7 anyway, why not have it make money for you in the process.

Once you earn a bitcoin you'll have to decide what to do with it.  I converted mine to USD using Mt. Gox. There was a .0005 fee to send my bitcoin there and then Mt. Gox took .30%.  Once I had it in USD I sent it to my dwolla account for .25 and then sent it to my bank account.  All said and done I got $13.70 of my $14.

Here are some helpful links to get started.

Bitcoin client
Python GUI Miner put this in the extra flags section: -v -w128
Slush's mining pool