Hi nadine2 - Actually, it is a very good question! The simple answer is, "You make up you own melody." I know that is not the answer you were hoping for, but that is the only one there is.
Generally, the chords and meter of the lyric might suggest a certain 'feel', but the exact feel might be different for each player. I posted a song several months ago for Valentine's Day (With You) that 2 other songwriters then recorded separately.
The results were marvelously unique - Upyerkilt's version was a great throbbing rock & roll take, and Roger Guppy's was a very soft and romantic folk version. Here is a link to that song's thread:
http://www.chordie.com/forum/viewtopic.php?id=1258
I think the links to the recorded versions are also somewhere in the thread.
So - use the bare bones of the lyrics and chords provided and let the spirit move you!
I also noticed your posting on the Oud thread - great stuff. The history of musical instruments offers us fascinating insight into cultural tides and technological advances. Here is nifty bunch of folks who like to make music on sackbuts, crumhorns, shriari, and other lovely relics:
http://www.waits.org.uk/
James
"That darn Pythagorean Comma thing keeps messing me up!"
[url]http://en.wikipedia.org/wiki/Pythagorean_comma[/url]