I was looking for a official comparision between the different VS2008 editions and thankfully I found it here.
The express editions are different downloads for each language. i.e. for C#, VB.NET
So if you want to open different projects in different languages, then go for standard or professional. Then the express editions do not have visual designers for WPF and WWF.
Some of the differences between the standard edition and professional edition are that you can use the professional edition to build MS Office applications. Also the professional edition has support for Crystal reports, Unit testing etc.
More information can be found at the following links: