I've got an old Dell that's running XP Pro and am also experiencing problems as far as Windows not recognizing the Epic via the USB connection. I purchased a generic cable that came with a cd rom w/ drivers, and after loading the drivers, Windows still won't recognize the device. I also d/l'ed the USB drivers from Samsung's site and that didn't work either.
OK, I had to call customer service to get this one resolved. I have an old Dell running Windows XP Home Edition Service Pack 3.
Make sure you have wifi and bluetooth disabled on your phone.
I did download the drivers from Samsung's website first.
Plug your phone into a usb port on your desktop computer. The phone will give you three choices. Choose the third one that says "tether mode." After that you'll see two choices. Make sure "3g dial up" is chosen if you don't have access to 4g. If you have access to 4g, then choose that option. The phone will inform you that you will not be able to use data on the phone while using "3g dial up." (or 4g dial up) Just click "OK." You'll still be able to receive calls even though it will sever your tethered connection...
Then on your desktop computer:
I had to set up a connection under the "network connections" window which is located from the "control panel" then click on "Network and Internet Connections" then click on "network connections."
Under "network tasks" click on "create a new connection." The new connection wizard pops up. Click "next." On the next screen choose the "connect to the internet" radio button and click "next." On the next screen choose the radio button that says "set up my connection manually" then click "next." On the next window choose the radio button that says "connect using dial up modem" and click "next." Then on the next screen you'll be given choices of which modem to use. Choose "Modem - Samsung Mobile Modem #2 (COM7)" then click "next." On the next screen type in whatever name you want to give this "ISP." I typed "Epic" and clicked "next." On the next screen, you'll be asked to enter a phone number. Enter #777. Click "next." Now you'll be asked to fill out user name, password, etc. Don't enter anything and just click "next." It will ask you if you want to create a shortcut on your desktop for convenience. I did. Click "finish." A screen will pop up and don't enter any of the information asked on this screen. Make sure that next to where it says "Dial" that #777 is displayed.
Then, make sure your screen on your phone is unlocked and on. (Don't worry after you connect you can lock the screen and let it go to black. Connecting just won't work when you don't have your phone's screen open. You'll end up with an alert that says "DUN Alert! phone is locked" on your phone when you click "dial". And on your computer it will say something about not being able to access and it will start counting down to redial.)
Now, click "dial."
You should connect.
I hope it works for you. It works for me.