We are remodeling our kitchen and want to remove 2 walls to open it up. We have a truss roof and want to know if we can remove both walls. One wall is part of the wall that runs through the middle of the house between the kitchen and living room, there are support beams in basement under this wall (we have a raised ranch) the other is wall connects to it and is between the kitchen and dining room. It is my understanding that with a truss roof, the load bearing is on the outside walls of the house. Is this true or is there a load bearing wall (the one that runs the length of the house excluding 12 feet between the living room and dining room)?

Can both these walls be removed without causing the ceiling to cave in on us?

The wall between the diningroom and kitchen is a partition, non-load bearing. Can be torn down. The other wall is "load bearing" technically. Your correct w/ a truss bearing on the exterior walls. That is why there are 2x4's zig zagging on the truss (webbing). Dead and live load is transferred through the webbing to bear down on the exterior walls. So basically the "load bearing" wall can be torn down w/o any header being installed. Make sure none of the trusses have been altered in any way before doing so.
As far as the ceiling caving in, it won't, but if you live in an area with snow, you may see drywall cracks in the ceiling with snow load on the roof.
The support beam in the basement is to support the floor system.
Note: when in doubt contact a structural engineer.

Also, before tearing down any walls make sure you know where your relocating any electrical, plumbing and/or heating pipes/ducts.