Here's the original(?) intro for it: on youtube with an orchestral overture.
On another site which talks about Hungarian Rhapsody being used in various cartoons, there was this, also:
Although this 1847 composition is widely used in Warner Brothers cartoons, it is not the Looney Tunes theme or the Merrie Melodies theme. The Looney Tunes theme is "The Merry-Go-Round Broke Down," written in 1937 by Cliff Friend and Dave Franklin. The Merrie Melodies theme is "Merrily We Roll Along," written in 1935 by Eddie Cantor, Murray Mencher and Charles Tobias.