Firstly, you will not be able to run both IE 9 & IE 10 on Windows 8 & 7. If you have updated or installed IE 10 on Windows 7 then you will need to uninstall IE 10 from Programs and this enables IE 9 on Windows 7. Most of people are comfortable in working with IE 9 than IE 10 since many web applications or websites developed are not yet modified to be compatible with IE 10 and this causes displacements or missing controls on User Interface of the web site / application. But things have changed when it comes to IE on Windows 8. Updated IE 9 to IE 10 enables you to access IE 9 just by switching the browser mode by following these steps. Launch Internet Explorer 10 then go to settings , click F12 Developer Tools ( or press F12 key) and you will see a small window tab opened at the bottom in IE 10. Here click on the "Browser Mode" and it gives you drop down list of browsers from IE 10 to IE 7. Select your needed mode and proceed with your work.
Note: You will have to repeat this step for each and every new tab opened if you have to run in IE 9/8/7 modes. Even after doing all this if your website isn't compatible with browser mode then you will definitely need the standard version without IE 10 in OS.