Here are two ways:

1. Through USB
1) Root Nexus One
2)Connect Nexus One via USB cable to you laptop.
3)Go to Setting, Wireless & networks, Tethering and then check on USB tethering.

Repeat 2),3), every time you connect nexus one to laptop thr usb cable for internect connection

*Important*
USB Storage should be turned off!!!!!

2. The seconde way is to be wifi connected.