I wanna be like you!!

Ok, a shout out to my blogging friends. I really want to put a big picture as my header on my blog and IT WON'T WORK!!! I've tried and tried... I upload the picture, click save and it ACTS like it worked...but then I "view blog" and its not there. I can't think of anything to make it work....SO, to you who know more than I, HELP!!!! Any bright Ideas? My header sucks, and yours are so cute. I want  to conform and follow the crowd, but I just can't!! Please, any tips! Don't let my persistent whining dissuade you from helping me. Thanks!!!