Open source network scanning / invetory / graphing tool?

[norbert_schuetz@bigfoot.com]

Hi folks,

is there any free tool for scanning and graphing (that is, 2D graph) a
LAN that will painfree run or compile under Debian? Or at least build
some sort of ip/device inventory for inital basic network analysis and
documentation? Possibly even with an option to add additional info
(room, hardware details, ...) manually?
For the need of every-now-and-then documenting a new customers network a
closed source windows-only software is not an option and also beyond any
- for the task - resonable price tag.

Any hints appreciated,
Norbert