Source: http://feeds.gawker.com/~r/gizmodo/full/~3/Oq96-w4GBiA/how-to-tether-the-g1-for-3g-laptop-browsing
We're not sure how well this method sits with your T-Mobile TOS, but a process has been revealed to share the G1's high speed wireless access with a laptop via USB. Configuring the necessary apps, drivers and settings is a bit more involved than a simple 2 or 3-step process, but it's all explained (and definitely followable) in the link. Actually, we'll put it this way: The method looks a lot easier than shelling out the cash for another 3G data plan. [TmoNews Forums via jkOnTheRun]