What about monitor resolution compared to a pc that the db looks normal on? If the db was created in a resolution that is the same as the "normal" ones and the new guy's is much higher res, then everything will appear smaller. Setting magnification to 150% might make the db more readable on the problem pc, but will blow up everything else he/she looks at.
As mentioned, if you're saying that the controls for all users are the same size but it's just that the font itself is smaller for only one person then it's not a resolution thing.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.