newbie developer creating custom object

[Erik Knight <kutuzof gmail com>]

Hi everyone, 

This is the first open source project I've ever worked on, so please
bear with me if I sound like a newb.

I plan to develop a custom object for Dia, similar to the UML objects.
I tried developing with just the .shape files and the text field
variable, but I need more customization than that. So I need to jump
into the C code.

Ultimately I need:

1) a box that maintains a minimum size, but grows if too much text is added.  
2) 4-6 text fields that can be edited by going into the properties
menu of the object.
3) 2-3 text fields that derive from mathematical computations of the
previous text fields. These should auto update each time the above
text fields are modified.
4) an image with a fixed size. The source of the image file should be
modifiable from the properties menu of the object.

What I'm developing is pretty specific to my needs. (my girlfriends
father wants a program that lets him maintain seating arangements for
his students and keep track of their marks. And lets him easily print
out everything. I need something to impress him to make my girlfriend
happy)

I'm not sure if the open source community as a whole will benefit, but
I do plan on documenting my progress and maybe this could become a
HOW-TO for developing custom Dia objects.

My question to you fine folks, is where is a good place to start? I've
already read through object.h and object.c and I've started skimming
through some of the other files. RIght now I'm thinking of starting by
modifying the chronogram or UML objects.

I have found the Wiki by Lars Clausen on writing programmed objects,
are there any other turorials or how-tos that exist out there?

Thanks for your help, 

Erik