Jumbo Frames

My company has an application that utilitizes gigabit jumbo frames for
tranferring data from a device to the local computer. We need to use jumbo
frames to obtain the performance we need. This works fine on XP and on some
Vista systems.

The Vista system that it works on is a low end system running Vista
Business. I have a high end laptop with Vista and it does not work. I've
tried Vista 32 and Vista 64.

The interesting thing is if I boot into safe mode with networking enabled,
it works. I tried booting with all services and startup programs disabled
and it didn't work.

Any suggestions? I have aero turned off. I wonder if Vista security is
doing something to "help" me out. I also have the firewall turned off.