Insert the Tascam US-1641 installation CD into your computer's CD/DVD-ROM drive and click the installer to perform the basic installation process. Before Cubase can recognize your interface, you must install the driver into the appropriate libary. With your driver installed, connect your Tascam to your computer using the USB port.
Open Cubase and click "Devices" on the menu bar at the top of your screen. Select "Device Setup" from the bottom of the drop-down menu.
Click "VST Audiosystem" in the left column of your setup window. An "Input" menu will then appear directly to the right, listing all of your recognized input devices. Select "Tascam US-1641" and click "OK" in the lower right corner.
Connect your musical equipment to your Tascam interface. Your XLR microphone jacks appear along the front panel and your analog instrument jacks (used for guitars, bass, analog keyboards and other instruments requiring 1/4-inch audio cables) appear along the back panel. Turn on your Tascam by pressing the "Power" button on the front panel.
Create an audio track in Cubase by clicking "Project" on the menu bar at the top of your screen and selecting "Add Track" from the drop-down menu. Choose the "Audio Track" option from the subsequent pop-up list and your new audio track will appear as a horizontal bar along your project window. Tracks function as recording spaces, enabling you to begin recording audio.
Record from your Tascam US-1641 to your Cubase software. Click the "Record" button at the top of your project window and begin transmitting music from your instrument(s) and/or microphone(s).