The key is your image editing software. You need to be able to resize your image by 'resampling' down to the correct image size (in this case, 540 pixels across) at 72dpi (computer screen resolution). Then, save the image as a 'JPG'. I use Photoshop, which makes this very easy. I've probably confused you further! Sorry! So, if you like, shoot me an email and we'll try to get it sorted out. Glad you like the flies- wish I could take credit for them.
Thanks for the tying tip, I'll give it a shot one of these nights.