You mean for multiple files open something like this :
Visual Studio's IDE is one of the most flexible around. You can basically pull the entire thing out into windows and move what you want, where you want, to make it the way that allows you to work most efficiently. You can hide and show windows and add custom ones, if you really didnt like the text editor, im sure you could get some form of replacement one as an addon feature, or even write it yourself.
The intellisense thing is a problem that I have aswell, and while im sure that it's something that is solveable, its not that big of a deal for me that I have bothered trying to solve it. The cause is due to the fact that intellisense is driven by a database that is stored and maintained by the IDE. This database is not updated constantly non-stop in real-time as doing so would cause slowdowns. Im not sure exactly how it updates, but im fairly certain that the way in which it is being updated is causing the problem. It tends to manifest more frequently for me while im in the middle of typing out half-complete functions and things like that(ie. the closing brace isnt present yet, or the function isnt prototyped yet), but not so often while im editting an already completed function....
I would reccomend sticking with Visual Studio though, as it is the "official" IDE for DarkGDK, and you will have a hard time getting DarkGDK specific support for another IDE as virtually noone else will be using it, not to mention that DarkGDK is compiled with Visual Studio itself so may not be fully compatible with other C++ implementations(Microsoft used to have a nasty reputation for it's c++ implementation not playing nicely with other implementations due to small "proprietry" features... I do believe that those kinds of things have been mostly eliminated(since v7 - v6.0 and below were the trouble makers), and MSVC++ complies quite well with the C++ standard now.) and those problems between implementations might not be able to be tracked TO the compiler as the problem, leaving you chasing your tail with seemingly unsolvable bugs...
That said, I do believe that if you wanted to get into the whole command line compiling, you could setup a different IDE to use the Microsoft Visual C++ compiler and linker(I have no idea how, but I do remember reading in a forums somewhere about a bloke using borland's IDE with MSVC++'s compiler and linker(many years ago, I think it was v6), though it looked like a technical nightmare for the poor guy to get going.)
If it ain't broke.... DONT FIX IT !!!