Best way to share files between to xp pro PCs across the internet

I have 1 PC with XP pro at home with a USB harddrive. The partitions on this harddrive are shared with other computers on my home network. This computer is behind a Verizon FIOS modem/router which is connected to the internet (non static IP I believe).

I have an office where I have another PC with XP pro that connects to the internet via a wireless router daisy chained to a router that connects to the wall for charter biz internet service with a static IP.

I want the computer in the office to be able to access the usb harddrive on the pc at home.

Can I do this?

Thanks,

Scott