Running Nightwing under legacy browsers
Nightwing is supported all the way up to IE7, but in case you want to run Nightwing under legacy browsers such as IE6 and below, you'll need to enable Attribute Selectors support.
To do that, I suggest you download Selectivizr and import it following their instructions.
Creating your own container
To create your own container with width you decide, just create a class with a name .container-xxxx and set a width for it. the "xxxx" part can be anything.
Now whenever you want to use the grid simply create a container element with this new class and insert row and span elements inside it. Nightwing will take care of the rest.
Feel free to reverse engineer, tinker with and customize Nightwing as much as you want, but please mention the original when doing so.
In order to change the gutter sizes in the gutter-enabled version, you'd need to recalculate the width for each span value + an IE value for it as well.
The difference of the gutter IE value from the normal one is 0.053191489361702%
The difference of the span width IE value from the normal one is 0.05319148936171%
It's not rocket science, really, just some basic calculator math :)