.net installation

hi,
i want to install .net in my system.
i have with me .net installion cd,.net disc1,.net disc2 and
other msdn installation cd's.i get an error like "setup has detected that
some of the system components that are installed on your computer do not
match the versions
required for visual studio .net.you must install a different
version of these components".
and also i am not able to install the prerequisites.

what do i do?
pls help me.

thanx,
kayal.