Registered: Jul 2003
Location: Brighton, Michigan, USA
Distribution: Lots of distros in the past, now Linux Mint
Well, ISPconfig is simply a control panel that allows you to make adjustments to your servers from the comfort of your web browser, and you can download it and use it, or pay for support if you desire, but as far as I know, it only deals with the server side of your needs, and you might want to look into something that may include support specifically designed towards working with MUDs.
That said, unless your MUD is going to be used by only a select few friends, you're best bet is to spend a lot of time and effort reading up on each of the servers you're going to use, as well as general networking information, with special emphasis on security, unless you enjoy reconfiguring systems on a regular basis. MUDs are like cracker magnets, partly because security on these systems is generally minimal, partly because most gamers are more likely to reinstall problematic systems than trace back problems and discover they've been hacked. (The way a lot of games are written has only reinforced this conditioning.)
In other words, while writing a MUD is complicated, it's just as complicated to manage the system the MUD runs on. (And this is true no matter what OS!) Aside from the infrastructure, you'll spend a lot of time managing chatrooms, email, forums, and then there's various troubleshooting and support stuff.
So, for anything more than a handful of friends, if you're new to the whole process, I'd suggest hooking up with a couple others, and splitting the load, as you're very likely to be overloaded very quickly if you try to do all this on your own. If you're totally new to the process, it might be to your benefit to join up with a currently running MUD (perhaps the one that got you interested in them?), and offer your help, kind of like an internship, till you're more familiar with the effort and expertise needed for this endeavor.
Not to turn you off to the process, but too many people set up MUDs thinking that it's an easy process, only to get overwhelmed. In general, it's best to start small, just having the minimum needed to get started (don't worry too much about a cool forum and auxillary items) and use close friends as "lab rats" to work out the bugs, and as you become more confident, then open it to a wider audience. At least then, you won't begin to hate the whole process, and you won't turn off other gamers in the process.
As far as Linux's abilities, not only does it include the servers you'll need to do this, but it's openness means you're going to have more flexibility controlling it in relation to your MUDs exact needs (more direct control over the OS means better response times and less lag for players).
No matter how you go about it, good luck!