you're going to log in as Admin. You should have been prompted for your tree name, password etc during install. So you'd log in as Admin.my_O or something along those lines.
Also, when the time comes, you don't need to make "trees" plural. One tree is all you need. The whole "forest" thing is a microsoft-ism. Forget that. Clear your mind.. one tree in eDir can easily hold multiple companies, locations, etc. It can scale to over 250 million objects. the whole 'trees' idiom is left over from NT Workgroups.. MSFT does not get it. Also AD does not partition while eDir does. This is important esp when syncing over WAN links. The more you learn about eDir, the more you'll appreciate it and what it can do. AD is rougly equiv to eDir 3.0.. (called NDS back then)
are you moving your whole server environment to Netware, or just migrating to GroupWise for email? If possible I would reccomend running GroupWise on Netware as opposed to Windows. Netware server licenses are free. You pay only by users, and each user can connect to unlimited resources and servers. (there is no 'per server' CAL equivilent in netware) GW leans heavily on the file system and disk access and will run far more efficiently on Netware (eg: more users per server, & faster response) Just a suggestion if you can do it.