Blakhart December 2010
isnt it a exe?
Turkeh December 2010
Unless you aren't using windows...you just double-click the Tribes2_gsi.exe file and it will install from there.
If you have somehow acquired a compressed version, we would need to know the file extension (.zip, .7z, .rar, etc) to begin helping you.
If you are running Linux or MacOS you will need Wine or similar to run the .exe file.