Outlook 2000-cannot Accept/Decline task

I have Outlook 2000 SP1 (internet only) setup on my Win 95 PC.

When I am assigned tasks, I receive them as plain text emails with a plain text email attachment.

When I assign a task to my coworker, he opens the assigned task from his inbox andit opens as a Task box with Accept/Decline toolbar buttons (standard toolbar | Actions)

Why do I not receive assigned tasks in this manner? All options appear to be the same in our Outlook setups.