I assume if your mum is having it then you will be putting a new Operating System on it. If so there is an option when you install the Operating System Disc to format prior to installing the new Operating System.

It depends where the Trojans are. If there are any in the BIOS then this method will not get ready of them. If they are in the registry, it should as you installing a new OS.

What is the Operating System you are currently running and do you have a burner on the machine? I would be careful about backing up the HD if you have Trojans and Spyware as most will go straight on to your new HD then. If you still want to go ahead you can create an image of the hard drive and then burn it to disc, then install it on your new machine.

I would get rid of everything you dont need though so when you create the image it is minimal. I did it at work and the machine image for a client machine, i.e it had nothing really on it was 3.7GB. Fortunately it was networked so I put it in a shared file and installed it on the new machine from that.

HTH