When I run the NS installer it says first thing:

"Setup has not detected a valid Steam install. Do you wish to continue?"

But I have steam and it is installed. If I ignore the message and install anyway it doesn't show up in Steam, because I'm assuming it's not looking for it.

follow the directions on the downloads page (or the better ones posted in the thread just below this one)

but basically one of these items:
1) you don't have HL1 installed. Yes, HL1, not 2 or source, HL1
2) haven't played HL1 (load up the training course and then quit out)
3) steam/HL isn't ACTUALLY installed (you reinstalled window or copy and pasted the steam install or any number of things like that)

I think it's maybe cause I have HL1 preloaded. I bought CS instead of HL which was stupid on my part. So it preloaded HL1 so that I can play CS. I think since it's preloaded it doesn't count as installed... Thank you for your help.

i have the same problem, but none of your suggestions worked. NS is really starting to annoy me now, ive downloaded about 10 different versions of it and none of them work

I think I linked this guide over 9000 times. Why aint it a sticky yet?

which is it? 5 mins before you made this post you made another post saying you would freeze at the load screen trying to make a lan game. this guy couldn't get the game to install presumably because he didn't have Half Life installed.

i'd like to know which 10 versions you tried because there is only 1 version you should be installing --> http://www.unknownworlds.com/ns/download/

Faskalia linked you to installation directions and they're very, very simple.