Add new column to production table

Hi,

I'm relatively new to SQL.  I need to add a column to a key table but there are many users locking the table.  I normally have to as users to log off but I cant imagine this is the only option.

The save operation times out when the table is locked.

Is there a way to add/modify/delete a column at any time regardless of who is using the table?

Thanks

Mani