SQL 2000: Query Question - Input Data Within Two Tables And 'between' Table

Hello specialists.

Maybe this is the wrong formum but I've got a question for which you probably have the answer, i hope.


Situation
------------
John is member of Group_A and Group_B
Bill is member of Group_B and Group_C
Allison is member of Group_A and Group_E

How can I create a query to input Allisons username into table 1 and groupmembership into table 2. Also updating the relationship within table3 must be done automaticaly. I want to avoid duplicate records.
The final situation I want is given in red text.

The relationships between the tables are as follows
-------------------------------------------------------------
Table1 (PK)ID-Userinfo [ONE] <------------> [MANY] Table3 ID-Userinfo
Table3 (PK)ID-GroupInfo [MANY] <------------> [ONE] Table2 (PK)ID-GroupInfo

Table1: UserInfo
------------------------------
(PK)ID-Userinfo UserName
1 John
2 Bill
3 Allison

Table2: GroupInfo
------------------------------
(PK)ID-GroupInfo GroupName
1 Group_A
2 Group_B
3 Group_C

4 Group_E

Table3: MemberOf
------------------------------
(PK)ID-MemberOf ID-UserInfo ID-GroupInfo
1 1 1
2 1 2
3 2 2
4 2 3
5 3 1
6 3 4


I hope you can help me cracking this nut.

Thx in advance. Greetings Fred