Welcome to... The Twilight Zone.

As someone who has worked as a tech support agent for a DSL ISP, I can safely say that this almost NEVER happens.

This has got to be the most bizarre workday that an inbound agent can ever have.

Scary revelation.

What if...

And I know this is scary, but...

What if Vista just runs piggy-backed off of XP, much like Win98 did with DOS?

It's the best explanation I can think of to explain a 15Gb installation for a bad Operating System.