You dont need WE Enhancer.
madcat, just make your image, it can be any file size, but the diminsions must be either 256x256 or 125x125. While 256x256 will give you superior image quality (Because 125 Will be stretched) it is a bigger file size, with me its usually 200 kb.
Get a free image program, such as "Infraview" (google it, its real helpful tool). Just open up your picture that you made (Jpeg,BMP,Gif w/e) and use "Save as" in infraview and save it as a Tga file (Truevision Targa).
Then import it into your map and give it the path "war3mapPreview.tga"
Thats it.