What's the native res of the LCD (the res the PC probably uses)? Make sure your Mac is using that too--it's the only sharp size.
Also, is the PC connecting via DVI rather than VGA?
Those are the only thoughts I have.
Re AtHomeBoy: the adapter should be exactly the same. But you can call Apple to make certain, or look the adapter up at store.apple.com (assuming they have bothered to update the product description since the MacBooks came out).
MacBook Pros use full-size DVI ports I think, but you're talking about the MacBook.