John, To accomplish the end result of what you want to do, there are two ways to do this. The less technical method and more secure would be to connect a router downstream of his DSL modem. Connect a cat 5 or faster cable to the router and run to your house. This requires another hole in the wall of the neighbors house. In your house you can then connect this to your computer. Terminating the end connectors is pretty critical with a long run like this. Instructions should be online.
Another approach would be to put a wireless router at your neighbors house, with security settings. Then Have another at your house and use what some call bridge mode. This lets the two routers talk to eachother over the greater distance. Then plug your computer into your routers network connection. NO Digging.
This may require special setup and software. I use a similar setup but shorter range. About 80 feet or so to the garage. I use a pair of linksys wrt54gs wireless routers. with Sveasoft firmware. This was done a few years ago and have no problems since. I am sure they have upgraded their software.
Look up
Sveasoft
When your sucessful convice your neighbor to boost his speed to at least 1 meg. you will be much happier with the setup.
Good luck.