Well A+ certification isn't going to get you far, you'll also need to be MCSE certified if you want a decent paying job. Your best bet is a full blown laptop so that you can put dual boot operating systems on it such as Linux and M$. Also you can usually find 0% interest financing at such places as Best Buy or Circuit City; makes buying a laptop pretty easy when monthly payments are $25.

Lastly, I don't know your situation, but at 26 years old you need to get on the ball here and the balls you need are not for buying a computer. The technology industry is a very competitive industry that looks for talented hard working people. Maybe you fell on some hard times that required to live at home, but at the same time I can't blame your parents for looking for rent money. Along with getting certifications I hope you are involved in a technical school as well.