64 bit option not coming

My machine is 64 bit. I have installed visual studio 2005, which by default installed in Program Files(x86). When i start visual studio I am not getting the option of win64 in the configuration manager. Please help me how can I get the option, do I need to reinstall it. I installed it 2 times but still the win64 option not coming. Please help. Thanks Sujan

Go to Configuration Manager. Click on "Active solution platform" combobox; select <New...>.
In a New Platform combobox, select x64.