If you're using Exchange you access it by opening Outlook, going to your deleted items folder (which will show in your folders list). If you're lucky and don't have your deleted items set to delete on exit form Outlook the distribution list will be in the deledted items folder.
If its not there, while in the deleted items folder go tools->recover deleted items and scroll though the deleted items until you find your distributin list, highlight the list, and press the button for recovering the selected item. The distribution list will recover to your deleted items and from there you can move it back where it belongs.
It only works if you're using Exchange AND your Exchange admin has a retention period set. We retain our deleted items for 7 days but it would totally depend on space issues, company policy, etc as to what your Exchange admin has yours set at.
Hope this helps.
Cheers.