CoqIde is a graphical interface for Coq. It is written in OCaml. CoqIde is documented in Chapter 14 of the Reference Manual.
Manual Installation in Debian
(See also the instructions in the file $COQTOP/INSTALL.ide in your Coq distribution)
If you want to install CoqIde but without using apt-get install coqide, in Debian lenny you can try:
$ apt-get install liblablgtk2-ocaml-dev
Then try installing Coq as usual using the instructions in $COQTOP/INSTALL.