Same as me...
I wanted a Mac for this exact reason. I solved the problem by paying for it ALL by myself! But, your the one who's right, not him. A typical laptop PC will last a maximum of 3 or 4 years, then it's bogged down, obsolete, and most likely broken (take my old Dell Inspiron for instance). My mom's iMac, on the other hand, works just as well as the day she bought it, can still run most modern programs, and isn't showing any visible signs of wear. She's had it three years two months. So, yes, it's worth it. It might seem like your paying less for the PC, but if you have to buy two of them for every one mac, your actually paying more. Plus, with a Mac, you get an awesome OS, and lots of cool little hardware features that you can't even get on most PCs. I assume your looking at a MacBook Pro 13", since you said $1400. I just got one, and can tell you, it's great. Way better than my sister's brand new Compaq laptop.
If your not planning on playing loads of games or doing some serious video editing, you might have a better chance of persuading your dad to get a White MacBook ($999) or the 2.2GHz model MBP 13" ($1099). Also, check out the student discounts <a href="http://store.apple.com/us/browse/campaigns/back_to_school?mco=NjcxMTQ3Nw" target="_blank">Here</a>
You can get $50-$100 off, plus a free iPod touch second gen.