Here's my understanding, meager though it may be:
d e f g a b c# d' = d melodic minor ascending
d' c bb a g f e d = d melodic minor descending
d e f g a bb c# d' = d harmonic minor (rarely used for melodies unless you're after a pseudo eastern european sound)
d e f g a b c d' = d dorian
These are the standard "textbook" modes on d.
What you might have, Captain, is a d dorian with a leading tone:
c# d e f g a b
If the notes in the tune are actually arranged that way (so the melody doesn't actually go above b, but you occasionally have d-c#-d) then I'd call it dorian with leading tone.
This is fairly common in American Sacred Harp tunes, actually. In fact some of them have
c# d e f g a b c (where the figure would go a b c b a, never up to the high d' from the c natural). It's a dorian scale except for the d-c#-d final cadences.
-Glenn