The object modell uses the Microsoft.SharePoint.*.dll, which are only available on a computer which runns SharePoint (WSS of MOSS).
You can use the object modell e.g. in a
Webpart.
Here are some common object:
Extension Methods
With extension methods you can extend the functionality of objects.
I have posted some commen tasks, so you can extend your objects with extension methods.
Samples --> SharePoint Extension Methods
To user the samples, simply create a new class in your project. It has to be public and static. That's it.
public
static class Extensions
{
...
}