To run Internet Explorer 7, you need Windows XP SP2.
Download Internet Explorer 7 (14.8 MB). You could also download IE7 from File Hippo.
Download the IE7 Standalone archive created by Jon Galloway.
Create a new folder IE7 in Program Files, copy the IE7 setup file and extract the files from the archive downloaded at Step 2.
Run the file IE7 Standalone Setup.bat and click OK to install xmllitesetup.exe, an update necessary so that IE7 has tabs.
Create a shortcut on the desktop to the file IE7.bat. Change the icon of the shortcut to one from IE7's iexplore.exe.
Now you have a standalone Internet Explorer 7 that runs along with Internet Explorer 6. You can launch IE7 from the shortcut you've created on the desktop. Note that not all the features will work well and this standalone installation is recommended only for developers that want to test IE7, but also need Internet Explorer 6.
More about this setup from Jon Galloway.
Internet Explorer 7 Review