You'll need Client Access running on the Citrix server, and a license for each user. I suppose the Citrix could have an SNA connection to the AS/400, but (and boy its been long since I used SNA) I believe you'd have to configure the Citrix server as an SNA controller to get multiple users connected to the AS/400 via SNA. But if you are using TCP/IP to link the Citrix and the AS/400 you should have no issues.