Generally we inclined to navigate X86 folder and use setup100.exe executable file to install the 32 bit SQL server, which leads to below error.
SQL Server 2008 setup100.exe and setuppatch.exe cannot be run in this mode. If you are running setup100.exe, start setup.exe instead. If you are running setuppatch.exe, run it from the command prompt, as the user interface is not supported for this action. For more information about Setup, see SQL Server Books Online.
Error code 0x84B20001.
In SQL 2008, Installer window is little bit different compare to SQL 2005. Instead of navigating to X86 folder, click on setup.exe and go to Option tab and select the architecture as shown below.