Visual-studio – Install Visual Studio 2008 Sp1 on “D” Drive

visual studiovisual-studio-2008visual-studio-2008-sp1

I am trying to install VS2008 sp1 to my work machine – it has a pathetic 10Gb C drive. The SP1 bootstrapper doesn't give the option to install items to D, only C. It needs 3Gb free and the machine only has about 700Mb.

VS allowed me to install to D originally why not the SP. The only thing I can think of that it requires system files installed in Windows etc, but I can't believe there are 3Gb worth of system files?