map it to an item and deform it. Is it posible? Like to import a pic of the flag and map it to a cube and then bend the cube to make it look wavy.
When you download file donot choose open use save as ,look in z brush file for textures thats where you will put textuer file,when you open z brush you will see on the sides textures open and load then pick texture you want to use,I hope this will help. Have a good day. 
Hi Acedrake . . . 
The answer to your question is YES. But there’s a lot more to the answer than that. It depends on how you plan on applying the texture to the object. I would need to know more about how you plan on using the texture on the object so I could give you an exact answer. 
As far as the “import a texture into ZBrush” part of your question, you can import any image into ZBrush, as long as it’s a .BMP or .PSD, by selecting “Texture / Inventory / Import”, & choosing the destination folder & file. 
Hope this helps some? Have a good one . . . Mark.
Kruzr’s answer was the simplest one.
Two notes to add that will help you out: First, don’t use a cube. Use a Plane3D. This will make it much easier for you to edit the way that you are talking about, and it will also make the texture itself easier to work with for this purpose. A texture wraps onto all sides of a cube, which means that you’ll have parts of the flag on every side, including the back, but never have the entire flag on one face. When wrapped onto a plane, it doesn’t wrap at all. Instead, it appears on the face of the plane, and is reversed on the back face – exactly like a real flag.
The second recommendation is to make your texture as a square before you import it to ZBrush. The best way to do this would be to resize your canvas (in your paint program of choice) to a perfect square, with the flag in the middle. Then on a layer below, fill the entire canvas with 100% black (#000000 in web terms). Then flatten/merge your layers and save your bmp or psd file.
When you import the texture, you’ll have a flag with black borders. In the Tool palette, select Plane3D, then in the Texture palette select your imported texture and click the Transparent Texture button. Now draw your flag.
The reason for doing it this way is that the Plane3D draws as a perfect square. As a result, your flag texture would normally stretch vertically to cover the entire square. Then you end up having to resize the square until it looks right. By using a transparent texture, everything that’s black simply becomes invisible and you get a perfect flag with no monkeying around. Of course, this wouldn’t work if your flag had any black in its design! But given where you’re from I’m assuming that you plan to use the American flag, which will be fine.
Hope that helps you out!