It really helps to mention what version of the program you're using. Not one poster here specified what version of NifSkope they're using. <_<
For the record, I use v1.0.20 (revision 4748) under WinXP32 sp3 and a separate app instance will open in a new window for each nif file I directly open outside of the app. You could also try right-clicking the nif file you want to open and see if there is a context menu selection for 'Edit NIF File' and select that instead of double-clicking the file (there should also be a context menu selection for NifSkope under the 'Open With' menu if NifSkope installed correctly).
I didn't think it would matter as I thought it would be an option. Ther version I'm using is "
nifskope-1.0.22.8329d39-windows.exe" which I downloaded from SourceForge which was linked to by the Niftools website. I'll try searching my drive for an older version.
I have tried the Edit nif option, I think I've tried everything actually
, but it didn't help. I need to open multiple intances as when modding I find it helpful to take screenshots of resources in a particular mod. That way I can skim through thumbnails or full pics to see if anything in a given mod might be useful rather than opening sometimes hundreds of models. This process is expidited when I can bulk select and open nif files.
Thanks for all your suggestions so far.