[Question] Setting up Types and SubTypes

Hi guys, first post here, I hope to get it in the right part of the forum.

I've been using ArcGIS software for some time, throught out college and now at work.

I have a doubt here.

I was given a task to make a .gdb where we'd join/merge several diferent datalayers, they're all points, from diferente types/categories of information, and we want them to be in one single layer inside that .gdb, so when we open it we have all the information, and the possibility to choose one type or another in a fast way.

We thought about Domains / Types / Subtypes, but there's a problem, I'll try to exemplify (my english isn't the best, sorry for that)

considering two fields, Field 1 will be the 'groups' and Field 2 will be the 'subgroups', I've managed to set up the 'groups' in arcgis catalog, and confirmed it in arcgis desktop, but I wanted the 'subgroups' to be dependant on the first field - 'groups'

in other words...when editing in desktop, after i set field 1/groups, i want field 2/subgroups to give me the options/categories related to it's respective field 1/group.

Categories as example:

Field 1 / Groups
Urban
Rural
Water

Field 2 / SubGroups
Industrial (urban)
Residential (urban)
Forest (rural)
Farm (rural)
Ocean (water)
River (water)

Hope i was clear on it...if you need anything, just ask, and if you can help, help :P

ArcGIS Version - 9.3

TY, cheers