There are a lot of artists that manage to make a mouse or trackpad work, but for beginning artists it's like running uphill when you're just learning to walk. I recommend sticking to traditional materials- pencil, ink, paint, marker etc. , and work on drawing and composition skills. You can document traditional work with a scanner or a digital camera, and then edit the image to your heart's delight in photoshop/gimp/whatever.
When you do get together enough money to buy a tablet, the skills you've learned working with traditional media will transfer right over.