Does the Targa have an existing Alpha channel? If so, use the alpha to delete the background and do a save as > PNG
If you don't have an existing alpha, you may be able to use one of the image's color channels to create one.
Windows pull done > Channels. Look at the individual Red, Green or blue channels. Find one that gives you good contrast and copy, create a new channel and paste. You may have to clean it up a bit, but this should separated the logo from the background.
Why can you just keep it as a TGA file with embedded alpha and bring that into your Non Linear? Some people call TGA files the Truevision Graphic Files because that is who made it. It is a format specifically designed to bring in high end image sequences into NLEs with alpha. They also save very well numerically as animated sequences to be used in video and gaming.