probably the easiest way would be to use an absolutely positioned div that sat above the image. The form would then go in that.
The best way would be to slice the image and put it as the background to the content area rather that have it as it is.
Looking at the rest of the pages suggests that you are going to have BIG problems with this site and the chances of seeing it on the search engines are very small.
in order to preserve the tables layout way, wrong as it may be, you have to split the first tr in three, making a six rows table, instead of four rows. that means that the initial first row will have 235px instead of 535, and the other two additional rows will have 265 and 35.
the tr in the middle (265) will be the one below Contact having the form you need.
also your Contacts_01.jpg image will have to be split up in three images accordingly, using the guides i’ve drawn in the image i’ve attached, and put in their respective tr.