When you setup your pricing to use 1 to 5 years, within the shopping cart you may well see something like :

£0.00 GBP One Time

This can be removed by doing the following:

Navigate to : templates/orderforms/web20cart/products.tpl

Look on line 34 for : {elseif $product.paytype eq "onetime"}

Change this to : {elseif $product.paytype eq "onetime" && $product.pricing.rawpricing.monthly > 0}

And that should remove it.