1) Which Ghost version is the earliest, supporting IGMP Multicast.
That would be Ghost version 5, in the 1997/1998 timeframe when IGMPv2 was brand new (IGMP, remember, was first standardized in 1989). In 1997 most switches were not managed, and when Ghost's protocols were designed IGMP was still primarily used in the way originally intended by its designers, to control
routing rather than switching.
Where can I find a tutorial how to configure the Cisco-3750 Layer 3 and several Cisco-2950 Layer 2 switches.
You probably won't find many tutorials outside of Cisco's own documentation, particularly in terms of mingling IGMP and VLANs; whenever VLANs are in use it's necessary to do some
very close reading of the capabilities of the particular models to know what you can and can't get away with.
I'm just looking at the
Cisco Multicast Support Matrix and I see that the 2950 does support IGMP snooping and does claim to support multicast in conjunction with it, so that's good. Which, incidentally, means it's not just a layer 2 switch (layer 2-only switches don't understand IGMP, which is at layer 3).
The most important thing related to IGMP to understand is just that if you enable IGMP snooping at any level (and as the table linked above shows, it's on by default in a lot of switches) then you
must also configure an IGMP querier which covers all the switches participating in snooping.
IGMP is fundamentally a host<->router protocol, and so you want some device (which can be the routing module in your backbone switch) to supply the router side of that, which is the IGMP queries. These queries are necessary to refresh the tables the snooping switches build as they learn which switch ports are involved.
[ The PIM protocol, which is the level at which things like sparse/dense modes apply, is a router<->router protocol and end hosts (and switches) don't use it. Some switches which include routing features may for their own reasons want you to enable it as part of configuring their support for multicast generally, however. ]
Should I configure the ethernet-interfaces or the VLAN-interfaces with this command?
The exact procedures to follow depend somewhat on the particular model and the particular revision of IOS (and for the many other vendors which follow the Cisco configuration command syntax, sometimes they have their own quirks too). It's best to consult the IOS reference for the specific edition of the firmware you have in each switch to look out for any gotchas in individual commands.
In general though, you'll be applying the commands at the VLAN level. There may for some commands be a need to enable a feature globally before you can also enable it at a VLAN level, but those should be noted in the command reference.
Is there a difference starting ghost from disk now? Do I need special command-line-arguments for ghost.exe, for example th server-ip? Or does Ghost client still detect the server without any parameters automatically?
In a properly configured network you will never have to do anything special. Ghost just follows the IETF specifications and in the IP multicast model, hosts have never been required to do anything special other than issue IGMP subscriptions and respond to IGMP queries. Provided the switches and routers are configured properly, everything Just Works, which is what multicast is all about.
Where you need to do things different is when you
don't have a properly working network; the -jaddr switch to specify the server IP is only required (or useful) in the absence of multicast.