I just wanna give feedback about my problem, descripted earlier. And thank you all for your support. My problem is solved.

I want to point the need of the KXRPC service on all dc's, although the manual says, it's not neccesary but recommended. My opinion is, that it's needed on all dc's.

Info;
-Domain called VANDRA
-PDC called VANDRA00
-BDC called VANDRA01
-BDC called VANDRA05

This was the situation:
I'd only installed the KXRPC service on Vandra00, the PDC, and made an KiXtart.ini file in the Netlogon Share's.

[KXRPCMapping]
VANDRA=\\VANDRA00
Default=\\VANDRA00

This is what the ini-file looked like. I'd used the following code to test the membership;

code:
If InGroup("Beheerders") = 1 ; Local Group
    ? "A member of Local Group!"
Else
    ? "Not a member of Local Group!"
EndIf

If InGroup("Domein Beheerders") = 1 ; Global Group
    ? "A member of Global Group!"
Else
    ? "Not a member of Global Group!"
EndIf
My problem was, that I couldn't reach the Global Groups with the service on, but could reach the Local Groups. When I turned the service off, I could reach the Global Groups again, but not the Local Groups. And ofcourse I'm a member of both groups. So I didn't use the service.

This is my new situation:
I've installed the KXRPC serive on all DC's. And deleted the KiXtart.ini file. And quess what. . ., it worked fine! All domain info is returned correctly for the few Windows 9x workstations on our domain.

Ryan