I did some Googling and found a few things that people recommend when installing other operating systems on a Mac.
1.) A lot of people recommend that you should not get rid of Mac OSX entirely. The reason they give is this: you will no longer be able to install any firmware updates. A parallel to this is people installing Linux on a Windows machine, then finding out there is a BIOS update available in the form of an .exe file, which is executeable only from a Windows OS.
2.)
Almost any Linux OS is free. Windows 7 Home Premium, the least expensive verion of Win 7, is about $95.
3.) You can install Windows on your machine fairly easily using Apple's Boot Camp software. And from what I've read, it's free. Were you aware of this?
4.) If you decide to dual boot Mac OSX and Linux, you should install Rod Smith's rEFInd first, before trying to install Linux. rEFInd is a boot manger capable of booting Windows, Linux, and Mac OSX on machines with UEFI capable BIOS. There are people who have Mac OSX, Windows, and LInux installed on their Macs, and claim this is one of the things that makes it possible.
One thing I've also found. The year 2008 was the year that Mac hardware and software made the transition from 32 bit to 64 bit. I believe 10.7 is the first 64 bit version of OSX, but want to be sure. Can you verify this? Also, do have installation media or is it possible for you to create installation media from your system? I think it would be wise not to burn all your bridges until you're sure how well Windows or Linux performs on your machine.
"When you rise in the morning, give thanks for the light, for your life, for your strength. Give thanks for your food and for the joy of living. If you see no reason to give thanks, the fault lies in yourself." - Tecumseh
This is due to the differences between Apple's and Microsoft's implementation of UEFI.