Trails/bike hire near Weymouth ?

[NakedGav]

I'm taking a group of scouts (14-18 yrs) down to Weymouth for a week in August and we're looking at hiring some bikes and doing a bit of riding for a day/half day. Nothing too strenuous as most of them are novices but just some nice trails would be good.
Can anybody with experience of the area recommend where to head for or any decent hire places ?

Thanks

Gav