Hello Max_C,
If the two devices are both using Messenger 2009, you can have them signed in both at the same time. This feature is called
Multiple
Points
Of
Presence (MPOP); it will mirror all conversations across all participating endpoints. On the other hand, if only one device is signed in at the same time, you can use a technology such as
Live Mesh to mirror chat logs (and other files) across computers.
Hope this helps you.