Assuming you have Photoshop, you can export you image as a jpg, gif, or my personal favorite png. Even if you could use your PSD file, they are much larger in size because of all the information that Photoshop includes with the file (layers, filter settings, etc.) which is information you have no use for. I usually save two files - the original PSD for editing, and an export as PNG for textures. If you don't have Photoshop, try some of the freeware viewers / converters like Irfanview
www.irfanview.com. Good Luck.
Art