Computer connectivity

My wife and I have networked computers for a home office. She is running Windows Vista and I am running XP. After about 8-9 days of being connected without difficulty, my computer will all but lock up when I attempt to send her a file or access a file from her computer.

She has to restart her computer (when this issue occurs her computer gets stuck on the "shutting down" windows screen) and has to be completely powered down and rebooted.

After her reboot, the network works great again for several days. Other computers are on the network, but we have not experienced problems with them (although we don't trade files between the others nearly as often).

Any ideas?

Thanks,
Chris