Try downloading.... as of May 4th 2011 will not work.
https://market.android.com/details?id=tether.android&feature=search_resu...
I am told Google is caving to pressure from Verizon Wireless, and will no longer allow users to download this app, preferring instead to force us to spend $240 a year ($20/month) to buy the tethering capability from VW.... IS THIS TRUE??? HOW ELSE CAN I GET THE SOFTWARE ONTO MY DROIDX???
1 - Go to the following webpage on your PC and download and install Android Sideload Wonder Machine :
http://forum.androidcentral.com/android-sideload-wonder-machine/40770-ac...
2 - Go to the following webpage on your PC and save the follow file as a .apk file:
http://tether.com/a/tether.apk
3 - Follow this video on how to install Tether on your Android:
http://www.androidcentral.com/sideload-android-apps-all-you-want-sideloa...