Jeff,
There is not a point and click way to make this change.
Mangetism has a good blog posting on it so I won't repeat it here. It is a pretty easy jscript insertion.
www.magnetismsolutions.com/.../default-activities-filter-on-to-all-dynamics-crm-2011
However, since you ajavascript:void(0);re trialing CRM 2011 you are probably online and that has UR12 installed so this code would be what you want.
www.magnetismsolutions.co.nz/.../default-activity-filter-on-to-all-dynamics-crm-2011-ur12