How hard is it to replace a cheap bathroom cabinet to a nicer, oak one?

I currently live in a mobile home and am trying to improve it cheaply, since I'm planning to sell it with in the next 5 years. I recently scored a very nice oak bathroom cabinet for free, but am unsure how to go about installing it. Obviously I need to remove my current one, but the oak one is about 1/2 inch shorter than my current one, and I already have the counter top in place. Can I do something to raise the new cabinets without making it look like crap? (Countertop is attached to 3 walls).