If you were closer it'd be easier, since pretty much all wireless access points have a range of 300 feet at the most without an external antenna.
If you have some money to spend, you can buy 2 wireless access points and 2 directional antennas.
If you're adventurous, you can try and build your own antennas.
The easiest, and cheapest one I've seen is made out of a Pringles can.
You can also use other types of tin cans as shown at
http://www.turnpoint.net/...
I think that the cheapest wireless access point is the Linksys WAP11.
It's supposed to be easy to add an external antenna.
Also, the WAP11 can be configured to act as a wireless bridge, basically pretending to be a CAT5 link between 2 points on a network.
Once you get the link up, you could just connect one end to the network at your school, and the other end to your computer at your house. Then specify the access point as the gateway for your computer.
Hope this helps.