The other day for one of our projects we needed to upgrade to SQL Server 2008. Part of the pre requisites was to have .Net framework 3.5 installed on the machine. The DVD had the install for the framework but it just wouldn't install.
The setup would unarchive all the required files, and fire the setup program. The progress bar would increase all the way upto 95 - 98 % and just hang. I am talking about the full package and not the boot strapper. Tried after a couple of re boots but exactly the same problem on a couple of my machines, all running XP Pro SP2.
Did some readups and a few people have had some install problems. The solution for this kind of problem is to disable all your network adapter. Go to the Network Connection menu, right click the connections and say disable. Once this is done, run the install for the full package, it should go through rather quickly with the Microsoft EULA popping up as soon the setup progress finishes.
Don't know why this happens, am assuming that the package still tries to verify if all parts are available for install and wants to connect to the net but is unable to do so through our proxy servers.
Either way, this workround works well. You would need to install the framework for SQL Server 2008, Visual Studio 2008 and going forward probably a lot more applications that get developed on the microsoft platform.
The microsoft page is here
The full package install is here
Hope this helps, do drop me a comment would love to know.