You've not stated when the vehicle was first registered. Prior to 1 March 2001, vans came under the 'Private/Light Goods' category. The tax on such vehicles is the same whether it's a car or a van. So you'll pay �99 for 6 months tax.
From 1 March 2001, cars and vans were separated into different categories. The tax for cars is based upon emission figures but there's a flat rate for the 'Light Goods' category. 6 months tax will cost you �96.25:
http://www.direct.gov.uk/en/Motoring/OwningAVe hicle/HowToTaxYourVehicle/DG_10012524
Chris