well ... it seems that the installer doesn't work correctly when downloading stuff from the net, but you didn't specify much information. That makes a diagnostic very difficult.
- You told alot about the downloading time, but didn't specify any error message you receive.
- You also didn't specify what operating system you're using (Win2k? XP? Vista? 2003 Server? Windows 7?) and the other not unimportant information (RAM size? free hard disk space? do you have any additional drives? which version of windows installer is installed?). For example, if you have a D: disk that is full, even if you install on C:, very often installers store their temp directory in the root of D: - and if D: is full, the installation will fail.
- Such a problem of corrupted downloads may occur if you've setup a wrong MTU/MRU value; maybe by a "network tuning" tool in your operating system, maybe setup manually in your DSL or cable router.
- If a specific step doesn't work out, what option fails to install? The MSDN component? The MS SQL server? Maybe you could download that separately and opt-out it in the setup?
If your download crashes, usually M$ is offering an "offline installer" or "redistributable" or something in that kind that doesn't download anything for most of their software. That file is definitely BIG (a few hundred megs!), but you'll only have to download it once. I didn't try it with VB2008, but just keep a look at download.microsoft.com - at least, it worked for me with vb2005 some time ago.