At this time, you can't paste HTML code or scripts directly into a Quark layout and have them export correctly as HTML. In order to get the PayPal HTML button to work, you would need to export your page and then edit the HTM document using an HTML editor. What I would do is take a screen capture of the PayPal Buy Now button and use that for positioning in Quark. Note the size of the box you place it in. Then using an HTML editor, like Komodo Edit (which is a free download), you can open your exported HTM page, search for the size of the box, and then replace the screen capture image with the HTML code provided by PayPal.
For example, the PayPal Buy Now button fits into a box that is 26 x 109 pixels. If you leave a spot for it in your layout, export the page and then open the page is Komode edit, that same box will be represented like this in HMTL:
td valign="top" width="109" height="26"
img src="image/Picture9.gif" alt="btn_buynow_LG.gif" width="109"
height="26" border="0" /div
Do a find for "109" to locate the code above in the HTM document.
Then you have to highlight everything from "img src=" to "border=0", delete it, and replace it with the PayPal button code shown here:
PayPal Button Code
Make sure you don't delete the opening and closing DIV tag. Your code needs to be placed between those two tags.
Save the file and then upload it to your web server and the button should work.