Let's start from the requirement. If I interpreted your needs correctly, you want to manage membership for an AD group through a SharePoint page.
There are multiple way to obtain this, I will try to list what comes to mind.
Option #1: event handlers on the list
Implement some update/insert/delete events handlers for the list. The handler will then contain the code to sync the new data with the AD group.
Pro: probably one of the simplest solution to implement, almost all complessity is in accessing AD.
Cons: unidirectional by design. You just act on some event that occurs on the list - there is no way to manage the opposite.
Option #2: timer job
Implement a SharePoint timer job that performs the required sync operations between the list and AD.
Pro: the sync operation can be made bidirectional.
Cons: Since you act in reaction to a state instead that to an event, it can become hard to decide the direction of an update: if the grup on AD contains an user that the list doesn't, it means that the user has been added via AD or deleted via list? Also notice that you might need to use the secure store to save some sort of credential for accessing to AD (you are in a timer job, which is run by the appropriate SharePoint process which may not have enough permission)
Option #3: external list
You could use an external list to map to the users in your group. That way, the two models - List on SharePoint and Group on AD - would be synched by design.
Pro: by design sync.
Cons: working with the Business Data Catalog is never fun. Could be manageable if you stick to c# based external list and SharePoint 2010.
Option 4#: drop the list, use a custom web part instead
If you don't really need the list, you could just drop it and develop a custom web part that manages add/remove of users to the AD group. This way the WP will be always in sync with the group.
Pro: again, sync is by design
Cons: you can do this only if you can drop the use of the list.
Those are some basic idea. Notice that you will still have to write the code that interacts with AD.
Could some of this options be applied to your situation? If you can provide some further input, I could offer some more insight on a specific solution or other unclear aspects.
EDIT: as requested, here are some more detail about the first option/solution.
As we said before, the idea is to use an event handler attached to your list to perform an unidirectional sync from the list to the AD group. I will give you a quick overview of the general implementation process: keep in mind that some of the steps I will describe may be automated by using Visual Studio/CKSDev projects/items templates.
Start by creating a class that inherits from SPItemEventReceiver. This is the base class to use when you want to create handlers that respond to item-level events on a list. In your case, we will override the default "empty" handlers for the item added, updated and deleted events.
After you complete coding the above methods, you will need do attach the handler to a list. As you may see from MS documentation, there are many way to do this:
- attach the receiver to a content type
- attach the receiver to a list template
- attach the receiver to a specific list.
All the above can be achieved both programmatically that declaratively via CAML. Anyway, in your case I would opt for the declarative approach: Visual Studio will create the default structure for you when you create a new project of type "event handler".
Having the event handler infrastructure attached to your list, you will be left with coding the actual methods for adding/removing the users from the AD group. This is out of the scope of this question, but you can easily find some sample around. This question comes to mind.
Last words: in my ranting above I have referenced events for handling item added/updated/deleted. As you will see there actually are TWO events for each group, one triggered before the action and one after: so for example you have item ADDING and item ADDED. By using this at your advantage you can cancel update events or detect update to an item.