An external 1TB HDD will retail for €100 including the case and USB cable.
The difference in prioce between a PC with 500GB and 1TB HDD is €50.
So I am afraid that somwhere, retailers are overselling what really should cost peanuts.
From this point of view, Amazon is a tue Peacemaker -
If Wally sells something for $100 and Amazon will deliver the same,
in three days, at half the price, you know whom to turn to.
As for Win7 / Win.VISTA, IIRC MS should encourage you to upgrade for very little cost.
Else, LINUX is, inho, a better OS than Windows.
What you want to watch out for is the slowy-pokey Celeron microprocessors
who claim they're 64bit, but are actyally the equivalent to the old "SX" chips of 386/486 fame.
In other words, Celerons should always be fed a 32bit OS.
They simply don't have enough teeth to chew on 64bit OS.
HTH