Finney,

This woul dbe a little more involved.  There are some things to consider:

1. When do you want the first recurrence?  If the field is changed on Wednesday, do you want the weekly reminders on Wednesday, or do you always want them on The first day of the week.  The same question applies to bi-weekly and monthly (what doy of the month do you want the reminder?)

2. What do you want done wit the old recurrence (if tehre is one)?  Do you want it deleted or updated?

3. What happens to the task if teh terms change such that the requieements no longer match?

I have not tested it, but a trigger would looks somethign like: 

Trigger createRecurringTask on Inventory_Terms__c (after update) {
    List<Task> tList = new List<Task>();
    for (integer i = 0; i < Trigger.new.size(); i++) {
        //Check if the task should be re-evaluated
        if (Trigger.new[i].Frequency__c != Trigger.old[i].Frequency__c) {
            if (Trigger.new[i].Frequency__c == 'Weekly) {
                Task t = new Task(Subject = 'test', isRecurrence = true, RecurrenceDayOfWeekMask = 2, RecurrenceType = 'RecursWeekly',
                                  RecurrenceDayOfWeekMask=2, RecurrenceInterval=1, RecurrenceStartDateOnly = Today(),
                                  RecurrenceEndDateOnly = Today() + 365);
                tList.add(t);
            }
            if (Trigger.new[i].Frequency__c == 'Bi-Weekly) {
                Task t = new Task(Subject = 'test', isRecurrence = true, RecurrenceDayOfWeekMask = 2, RecurrenceType = 'RecursWeekly',
                                  RecurrenceDayOfWeekMask=2, RecurrenceInterval=2, RecurrenceStartDateOnly = Today(),
                                  RecurrenceEndDateOnly = Today() + 365);
                tList.add(t);
            }
            if (Trigger.new[i].Frequency__c == 'Mothly) {
                Task t = new Task(Subject = 'test', isRecurrence = true, RecurrenceDayOfWeekMask = 2, RecurrenceType = 'RecursMonthly',
                                  RecurrenceDayOfMonth=1, RecurrenceInterval=1, RecurrenceStartDateOnly = Today(),
                                  RecurrenceEndDateOnly = Today() + 365);
                tList.add(t);
            }
        }  
    }
    insert t;
}

The above will create a recurring series for teh next year if teh picklist is changed.  The weekly and Bi-weekly fire on Monday, the Monthly fires on the first day of the month.

There is more information in the documentation also - 

http://www.salesforce.com/us/developer/docs/api/index_Left.htm#StartTopic=Content/sforce_api_objects_task.htm?SearchType=Stem

Hope this helps.

Jay