I suggest you read the FAQ on sunfreeware.com - especially question 7.
When you download from a site, normally they have the answers to these questions.
As far as a pkgadd in Solaris, normally if you don't answer yes, then the package does not get loaded. You will find that the gcc installation will have to put files in system directories. There may be solutions to this in the FAQ on
www.sunfreeware.com