Customize header or signup html?

I want to get a site logo and some signup instructions above my signup page. I've got it looking right in signup.html, but when I upload it, I have 2 problems:

1) You click on the link to the signup page, and you get prompted to enter a username and password before the page loads. Previously, the auto form filler dropped down after the page had loaded. As it is, it looks as though you need a password to get the page to load, which peopel who haven't registered won't have. If you click "cancel" the page loads ok anyway, but it would put people off, I'm sure.

2) My logo won't show. The alt text is displayed, but no image. There is also no box suggesting that the image is missing - just the alt text.

Should I be adding this to the header file instead? My only problem with that is that I want this info to be on the signup page only, not all the others...

Thanks.

Edit - I've just tried the same with the Header, and get the same problem. My main worry is the fact that the autofill box drops down before the page will load, because I think this will put people off.