re sub help

[s99999999s2003 at yahoo.com]

hi

i have a string :
a =
"this\nis\na\nsentence[startdelim]this\nis\nanother[enddelim]this\nis\n"

inside the string, there are "\n". I don't want to substitute the '\n'
in between
the [startdelim] and [enddelim] to ''. I only want to get rid of the
'\n' everywhere else.

i have read the tutorial and came across negative/positive lookahead
and i think it can solve the problem.but am confused on how to use it.
anyone can give me some advice? or is there better way other than
lookaheads ...thanks..