I believe it would go something like this:
* You want to barter for a 1000 USD pc located in the US and pay 1000 USD worth of gold.
* In Norway you then pay 1250 USD for that weight in gold (1000 USD for the gold, 250 USD in vat) and send it to the US.
* The pc is sent to you, but is now worth 1250 USD because that was what you paid for it, so you pay an additional 312 (25%) in custom duty.
* Making your 1000 USD pc costing you 1562 USD.
So bartering with assets like gold and now BitCoin may not be a good idea as a private citizen. Companies of course are exempt from vat, so other rules apply.