Correct me if I’m wrong, but Photoshop can open vector files. Is that not all that is needed to design a banner? Unless you need to save a vector file, I don’t think you need Inkscape/Illustrator.
@blessingscaptured, how do you plan to print this banner? Your printing company should certainly have guidelines available for what sizes and resolutions you need…
Based on VistaPrint’s and Banners.com’s specs, it looks like you only need 150 DPI for a similarly sized banner. (i.e. 10,800×3,600px)
Make sure you have plenty of room for bleeds, of course. 🙂