Problems installing SQL Server Express 2012 to Windows 7

Hi,
I am trying to install SQL Server Express 2012 with tools to Windows 7 64 bit on my laptop and I have Office 2010 32 bit..  I downloaded from the 32 bit SQL Server choice.  I get the following error:
"The operating system on this computer does not meet the minimum requirements for SQL Server 2012.  For Windows 7 or Windows Server 2008 R2, Service Pack 1 or later is required."  I checked and my Windows 7 has not automatically updated to Service Pack 1 and will not do it automatically.  What should I do?
I've considered downloading and installing SQL Server 2008, but which one should I download?  What is the differences in the versions?  Which one is for Windows 7?
  SQLEXPR_x64_ENU.exe                82.5 MB        &n ...