As Steven V said, there are considerable differences.I came here looking for a solution to this question precisely because things were running fine in IE9 with 7's browser and docmode but the actual IE7 was crashing completely.You can't install it natively since Internet Explorer 8 is already part of Windows 7.
Another option would be to install Internet Explorer 7 within the Virtual XP mode, provided you have at least Windows 7 Professional.
While you can't install IE7 on a Windows 7 machine, there's a program called IETester which provides historical versions of the Trident rendering engine (the core of Internet Explorer).
IE7 is included as one of those historical versions, so you'll be able to evaluate how a site renders, without needing to actually run IE7 itself.
Well sit down, in front of your computer, and start downloading.
We have several new j Query releases for you to test.
For your convenience, j Query can even be downloaded while standing.
First up are the final versions of j Query 1.9 and j Query Migrate 1.0.
We think these releases are pretty solid, because very few of you reported any problems in the beta versions.
Just be sure to read the information in the j Query 1.9 upgrade guide so that your transition will be smoother. Today you get a glimpse at the future, and it’s bright. We know it’s a lot to take in, so let’s recap the positioning for j Query 1.9 and 2.0: The j Query Migrate plugin can be used with either 1.9 or 2.0 to detect deprecated and removed features, or to restore old features for those sticky situations where you need old code to run with new j Query.