The tax (vignette) is a sticker to go in the windscreen. For a vehicle under 3.5 tonnes you can buy it at the border for CHF40 (currently around £22.50) or you can order it online from Swiss Rail's office in the UK for £21 plus a £5 admin fee - go to http://rail.myswitzerland.com/index.php?system=GB and scroll down to near the bottom left. Trailers and caravans need their own sticker and heavier vehicles have different arrangements and can't be done online. Stickers are issued for given year with an overlap into the previous December and following January - don't do it now for a 2009 sticker!

The official site explaining the rules is http://www.ezv.admin.ch/zollinfo_privat/informationen/00421/index.html?lang=en and the blue link at the top right "map of motorways" shows the roads covered by the tax - if you can avoid these you don't have to pay. The left side menu item "motorway tax sticker" shows where in the windscreen it has to be placed - you can be fined for not properly fixing it even if you have one.

Thanks.

When you buy your motorway tax vignette at the border, the vendor puts it on the correct part of your windscreen. Note that you cannot pay in sterling at the border - at Basel they will accept Euros or Swiss Francs.

There's really no point in avoiding motorways in Switzerland. They take you where you want to go .... directly, without fuss and are kept in very good condition even in the winter.