Fixed layer at bottom of page WP, with page scroll

I need to do a WP site with fixed size (vertical and horizontal; ex.: 1000 x 600 px) but with content that exceeds this vertical size (with scrollbars). I need to have a fixed layer at bottom of WP site, with scrollbar (like the black WP admin menu bar, just at bottom of page).
There is a plugin to do it or I should make it editting the WP PHP files?

There is a exemple of I want at:
http://sonora.terra.com.br/
1) type at “Busque por artista, álbum ou música” an artist name (ex.: Elton John) and press “Buscar”
2) croll to bottom, and click at play button (>) at left side of a music name (column “selecionar todas”)
3) the fixed layer appears, with music player; scroll the page to bottom: the fixed layer stays abover the page scroll