craftgrrl | My sewing machine = bonkers

So the sewing machine I borrowed for an indefinite amount of time from my mom's cousin has...issues. It's a fairly old Singer model, and it's nice and all, but I'm beginning to think it cannot sew a straight line. At first I thought I was doing something wrong, but now I'm 99% certain that the machine makes my fabric veer off to the left unless I pay close attention and guide the fabric back to the right. My question is thus:

Is this fixable? I'm looking for a) long-term fixes, no matter what the price (because if all goes well, I will own this sewing machine soon instead of 'borrowing it forever') and b) a short-term fix (in the rare event that I *do* have to return it)