SQL SERVER 2008 installation issues

HI

all

--I have installed visual studio 2008 professional edition installed on my computer , it works properly

--Last month I installed visual studio 2008 service pack1

-- 2 days ago I installed sql server 2008 management studio 2008 express evaluation edition , I was thinking of installing enterprise edition ,

but made a wrong download

Now how will I install SQL SERVER 2008 enterprise edition

It shows an error "Microsoft Framework 3.5 setup failed"

Please help