as written in theHow do I upload a file which is not added directly to iWeb and what will its URL be?
chapter of my E-Book I would recommend you to have a folder called "media" (without quotes) where you upload all the non-iWeb stuff and put this folder into your iDisk/Web/Sites/ folder.
The URL of this folder will then behttp://yourdomain.com/media/
if you put an image in the media folder let's call it paypal.gif the URL will behttp://yourdomain.com/media/paypal.gif
and entering this URL into your browser will display the image in your browser.
In the PayPal code you always see two URL of images. One called pixel.gif (which you should not change) and another one which I put in red in the following code:
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="5HMUEPE4UHL8C">
<input type="image" src="https://www.paypal.com/en_US/CH/i/btn/btn_buynowCC_LG.gif
" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
and which is the one which you have to replace with the URL of your own button if you want to change it. The URL of the PayPal button may look slightly different in your case but it's just the only .gif other than the pixel.gif so you should be able to find it.
Hence replace the PayPal button's URL with your own URL and that's it. You can also enter the URL to your own button when creating the button on PayPal's page under Step 1, Customize text or appearance, Use your own button image.
Whether you use a .gif or .jpg or .png doesn't matter. .gif is recommended because it's light-weight and allows transparency whereas .jpg doesn't.