If you look at the dates on the Wiki for Fargate, the earliest page is on July 08, FMud was released in May.
Other than that, it kind of seems to me like you're leaping to a potentially unfair conclusion. The display elements for both clients are what I would consider bare-bones basic, hard to draw a case for potential theft there. I guess the question is what do you mean by almost identical? Isn't that true of most MUD clients in that they pretty much all do the same basic things?
Lastly, if you take both developers at their word, Fargate is using Flex (which for some reason I've also seen referenced in Java books) and FMud is using ActionScript directly. They both boil down to the same thing, really, but it's worth noting because the programming approach is different - like using XAML for GUI rather than pure C#, in .NET speak. (Actually it's almost exactly like that =x)
Anyway, it's all moot unless FMud's creater shares his code, which - frankly - he doesn't need to.
No, FMud is not related to the Fargate client. The reason they look similar is that they are both built with the Flex framework using its default theme and widget set.
I don't know why you'd post here for an answer when you could have just emailed me and asked. Also, if you tell me what you didn't like about the last version of FMud I can see if I can change it, although if it was the line spacing that has been fixed in the latest version.