If you're moving for Stability and Uptime, I would advise Doing it in several steps.
I suspect that the NT server is down most often, so start there. Set up a Linux Box, and get Apache, FTP, and Sendmail (or whatever applications) all working well. Then dump the NT box.
Personally, I like Netware, and if you're running Netware 4 or better, I'd suggest you keep it. NDS is a great benefit, and with Caldera Linux in particular, you can keep the simplicity for the users that comes with Netware and NDS, while using Linux for App serving.
If after you have the NT box gone, you still want to move to Linux for File and Print, you will want to use Samba for File and Print on the Linux box.
Have fun.
Kev.