Rode condenser mics are good. You should of went for the NTA2 instead of the NTA1, but it will be good enough.
I have some background in this subject, I use to produce songs and all that. I usually did a few things to ensure good quality. First, I set up a blanket behind the mic and (if I had the time and space) behind the artist. If you're mic is placed on a desk you can try stacking pillows behind it. You also have the option to build a small (and I mean small) box to place your mic in.
See this link to build one:
http://www.youtube.com/watch?v=p_QJrcWdFgs
These materials you place behind and around your mic will stop your recording from sounding boxy and it'll reduce some small echos.
After I have all that set-up I usually start recording. Make sure when you record you're comfortable. You might have the play with the positioning of the mic to get the volume just right.
I used a program called Reaper to record, but that was more for producing songs and stuff. I'm not sure how it works when screen capturing and recording so I can't give you any info on that.
Post-recording editing is important. Listen through the track. You can always replace, edit, and delete existing material so don't worry about messing up. I played with the levels a lot and ran the track through multiple filters to get the right, clear sound. I don't remember exactly what I did, but just find some youtube videos or articles that work with the software you're using.
If you have any questions then let me know. If you know what software you're going to be using then please let me know and maybe I can help you out with the best settings and what not.