Why use Photoshop? Why not use the Pen Tool in Illustrator to create a path around the logo? Just remember to add a new layer to the logo file once it is opened in AI, lock the logo layer and use the Pen Tool to trace around the logo on a new layer (or several layers if the logo is complex). You can turn the logo layer on and off to see how you are progressing and which bits you've missed, and then once it is done, delete the original logo layer.