I have a gorgeous, maybe overfriendly collie (sam)! He initially is very good off the lead but when he sees other people or dogs he immedietly races over to speak to them (he's very friendly not aggressive),we can't seem to stop him doing this!Any suggestions?

Also... my mum has horses and when we take sam up to the field to get them we can't seem to stop him chasing them and using his rounding up instinct to round them up! any ideas?

Most obviously is the requirement to keep him on the lead.

And regidly instill in him the discipline to sit immediately when told to do so, even from a great distance. That way, when he takes off across a park to make friends with anyone you can get him to sit before he gets too close and scares the people he is racing up to. As you may well realise, an unknown dog racing up to a complete stranger can lead that stranger to think they are going to be attacked, and make an official complaint about your dog being dangerous, and uncontrollable.

It sounds as though your dog is from a working strain of collie, and so you are going to have your work cut out for you.

There is no way your dog is "safe" to let off the lead in the countryside. With his herding instincts so close to the surface, he could well end up getting shot by a farmer if sam is seen to be apparently "worrying" sheep.