For WebOffice 10 R3 ArcGIS Server Standard 10 with at least SP2 needs to be installed and licensed. ArcGIS 10 SP4 is recommended!
With WebOffice 10R3 SP1 and later ArcGIS 10 SP5 is also supported and recommended.
It is recommended to install ArcGIS Server .NET because setup and post installation are easier as for ArcGIS Server JAVA.
More information can be found at the international Esri website:
http://resources.arcgis.com/content/arcgisserver/10.0/arcgis-server-server-requirements
In general it is recommended to use local accounts for the ArcGIS Server post installation and the ArcGISWebServices account for accessing the services. Do not use accounts with expiring or permanently changing passwords for post installation or service access!
For the usage of WebOffice 10 R3 printing, uploading local geodata and geoprocessing in a distributed server scenario it is recommended to use a dedicated domain user service account in post install process instead of local ArcGISSOM, ArcGISSOC and ArcGIS Web Services account. On details how to post install with domain user accounts see the Esri knowledge base and help articles:
http://resources.arcgis.com/content/kbase?fa=articleShow&d=36535
Supported combinations of OS and ArcGIS Server concerning multilingual installations:
•English OS, English ArcGIS (Server and Desktop)
•German OS, German ArcGIS (Server and Desktop)
•German OS, English ArcGIS
Note: Different combinations will not be supported!