[jaak]

There are only about a million threads covering this, you would do well to do a little research.

However, the simplest and easiest way is as follows (if you are using Sprint):

Since you are using XP, you need to have ActiveSync installed.

1. Disconnect the USB cable (if connected).

2. Establish a data connection on the phone. The easiest way is just to start Pocket Internet Explorer.

3. Go to Programs and run Internet Sharing. Make sure the connection says "SprintPCS" (it's debatable whether other options really have a negative effect).

4. Press connect. If you get an error it's because you didn't follow step 1 or 2.

5. Connect the USB cable, your laptop will automatically see the internet connection and do the rest.

Lastly, if you don't have a Phone as Modem plan, there is no guarantee you won't get charged for tethering. However, as far as I know no one has (except people who download massive amounts of data or connect to a different data service (ie. dial other than #777)).

There are other options for doing the above that involve registry edits (makes it so you can skip step 2) or 3rd party programs (makes it appear as though your phone is requesting all the data, rather than a tethered computer).