troubled with queries

[binary_dreamer]

hi. i got a task to finish, but i am not sure on how to implement it. the task is:
there is a database of 54 entries (with the option to add/remove entries). those entries will be in three groups ABC. group A will have the first 13, group B the next 13, and group C the rest. i want to have a script that for Monday to Friday will take from group A, one everyday and in serial mode. for weekends it will choose:
Saturday: one from B and one from C
Sunday: one from B and one from C.
this is for two months. after that period the groups rotate so it becomes:

weekdays group B
weekends group c & A.
then the next two months will be:

weekdays group C
weekends A&B.
any ideas on how to help me on that task? i am confused with the queries of php on MySQL.

thanks in adavance.