Installing Visual Studios using Bootcamp Assistant
BootCamp Assistant is only for installing the OS, or burning the drivers CD used to help you complete the installation of drivers for your particular hardware.

Once you have a working Windows 7 install, Bootcamp just provides the facility to boot between the two OS, Windows and OS X.

In this case, you have successfully completed the install of Windows 7, but you are having issues installing VS2010.

Whatever the install issues with VS2010 Express are they are unlikely to be related to the fact that Windows is running on a Mac, and more than likely to be install pre-requisites, such as service pack level, etc.

Without further information its unlikely that we would be able to determine what the issue is, or if it is in any way related to being run under Bootcamp.  Have a look to see what the install.log said.