You have basically 3 choices. The 1 I prefer is terminal services
which allows the remote user to log into your machine or better
yet a server and directly update data. I like this because there's
rarely and conflict resolution problems. I use RDP built in,
Windows Terminal Server, if I have a lot of users, or lately,
WinConnect:
http://www.thinsoftinc.com/product_thin_client_winconnect_server_xp
.aspx
The next choice is using aan asp or similar web service to connect
to the data. I dislike that one because it is expensive to write
and maintain by comparison to other choices.
Lastly, there is Access replication which allows you to sunc up
data from multiple separate sources.
http://support.microsoft.com/default.aspx?scid=kb;en-us;182886