You can download it from here:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=6a04f16f-f6be-4f92-9c92-f7e5677d91f9
You run the setup.exe in the folder where you unpack the contents of the download.
I have Windows 7 Ultimate on an Aspire 4810TZ-4011 notebook which also has a number of SQL Servers both Enterprise evaluation as well as SQL Server Express.
This time I installed a named instance Hodentek3\Alaska and after starting the install I went to bed and in the morning I saw success staring out of my notebook. No problem at all.
Here are some screen shots,
