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Which version of Linux Mint are you using? I guess you still have Linux Mint 12, and not the just released Linux Mint 13. You need not suffer Gnome 3 on Linux Mint 12
At the login screen, click the little gearwheel icon in the top right of the login box. Select MATE. MATE is the continuation of Gnome 2, you should be right at home
Though perhaps worth upgrading to Linux Mint 13 MATE, http://www.linuxmint.com/download.php
, as that brings improvements over Linux Mint 12 and is a long-term support release, with support till April 2017.
Alternatively, on Linux Mint 12 open the Software Manager and search for Cinnamon. Install it. Then again at the login screen, select to run Cinnamon. Cinnamon is the new desktop being developed by the Linux Mint developers. Though it runs on the modern technology offered by Gnome 3, it looks and behaves more like the "classic desktop paradigm" as offered also on Gnome 2 / MATE.
Here is the announcement of both Linux Mint 13 MATE and Linux Mint 13 Cinnamon for some comparison: http://blog.linuxmint.com/?p=2031