Why should you move the client’s AS400 into your office ?
Anyway, there are ways to communicate between different physical locations and use an AS/400 via private data lines or via internet. Obviously, if you communicate thru Internet there must be proper firewalls and preferrably VPN type connection between the remote and local LAN.
If you need to use AS/400 native applications and have access to databases, you can install IBM Client Access package. It contains a 5250 type emulator, file transfer routines and some other tools for using AS/400 databases directly, e.g using ODBC routines with MS Excel or some other tools.
I’m using two AS/400 machines remotely almost daily, other one thru ADSL line and other thru an ISDN connection (a dial-in link to my customer’s network)