I think you should take a deep breath and really think about the money you spent and the effort you may be required to expend. This forum can be very helpful. The problem with your question is that the people answering questions are just people who had nothing to do with getting you into the situation.
So starting off that you are going to sell the machine is a tough insult to take right away. We can certainly help you if you are willing to try. If you have already given up then there is no point.
All of us spent the same amount of money to acquire the various hardware we have. Many of us have spent numberous hours solving many problems for ourselves and others. I suggest you give the forums a try and Apple support at an Apple store:
Heres the list: http://www.apple.com/uk/retail/storelist/
Is the ONLY problem you have that you don't have MSN messenger (as a side note MSN stands for MicroSoft Network and is a DIRECT competitor to Apple)?
I used a Google search for "MSN Messenger 8 Mac OS X" to locate the installer:
http://www.microsoft.com/download/en/details.aspx?id=4740
I confirmed this would install on my machine (MacBook Pro 15" running Mac OS X 10.7.3). I hope you will consider hanging in a little longer.
Best regards,
Wayne