Error 1330.A file that is required cannot be installed because the cabinet file c:\new folder\cab1.cab has an invalid digital signature.  This may indicate that the cabinet file is corrupt.

I have been trying to setup a new windows xp virtual pc environment for the past few days and every time I tried to install Visual Studio Team Suite 2008 I kept getting error like the one above about cab files with invalid digital signatures.  I tried different methods to get this to install.  First I tried to capture the iso located on the host using the virtual pc feature, this did not work.  So then I tried mounting the iso within the virtual environment.  I then tried to capture the host's CD cdrom.  Each time I would also clear out the %temp% directory.  Finally, I tried copying the files from the host's cdrom to the local virtual environment.  No matter what, I would get strange errors that the digital signatures were not valid.  I even checked each cab file's signature locally to make sure it was valid and if it wasn't I copied that file over again until it was.  Even though they were all valid at this point, once I started the install I still would get the error.  This didn't make any sense because I have used this cd to install Visual Studio on another machine before with no problems.  Since I have a dual boot system running Windows Server 2003 and Vista, I tried booting the host into the other OS; Vista in this case, I got the same results.

I then remembered this article (http://4sysops.com/archives/why-windows-vista-only-sees-3gb-memory-in-a-pc-with-4gb-ram-and-how-vista-sp1-fools-its-users/) I came across when I was upgrading my machine's memory about how 32 bit machines can not take advantage of 4 gb of memory.  I had recently added more memory to my machine giving it a total of 4 gb of memory.  Even though the OS wouldn't report 4 gb I kept it in their because I had no other use for it.  Well when I took out the extra 1 gb in the machine as a last ditch effort, Visual Studio 2008 installed with no errors.

So the end result is if you are getting these errors in a virtual machine and you have 4 gb of memory installed on the host, try removing 1 gb and see if that solves your problem.  One last note, I was installing from the host's cdrom when it finally installed but I assume the other methods would also work now too.