Can you Insure yourself to drive a car you don't own ?

[Igovernor]

and I thought you were just a computer nerd

If you have fully comprehensive insurance yourself then you are covered to drive another car but only on third party cover. As for your original question
Yes you can insure your moms car you do not have to be the owner or registered keeper, I have done that many times. What you can do is one of two things
1 ring the insurance company and add your name to your mams policy
2 ring up the insurance company and tell them you want to take out a policy in your name on your mams car.