Getting a copy to practice on is the most important thing. When I did my BEng 9 years ago we didn't do any formal training in any drawing software, we were expected to go and learn it ourselves, so I feel your pain!
You dont have to use AutoCAD, but in my opinion it is the best. Some people use Google sketch up which is free.. (I haven't seen a professional construction drawing to BS 8888 using it yet though!) you could try Microstation.. there are loads. But ultimately, AutoCAD is best in my opinion.
Going back a second, before you work out how to use AutoCAD you need to understand exactly what a drawing should look like. Many people miss this seemingly obvious point! BS8888 is the British Standard for 'Technical product documentation and specification' and provides best practice guidance for the production of construction drawings. Many Scaff designers don't even know this exists. You can tell the ones that do, as they drawings all look very similar, as depicted by the code.
So, going back to how to use AutoCAD.. I would suggest two things:
1. Find "LYNDA" training video's online. They are as good as any.
2. Ask people on your course if you have access to forums or discussion boards etc - chances are there is a professional draughtsman on there, you would learn more from them than anyone. Professional draughting is a dying art, they could teach you in one day shadowing more than you could learn in a month of online tutorials!
Also.. fair play for doing the BEng through OU, the hard work will pay off. If you ever need any assistance, call our office and ask for Ben.