If my keyword/phrase Domain is, for example, "yellow pens"...I want, and need, that term. but YellowPens.com is taken, and Yellow-Pens.com is also taken. Yellow--Pens.com is available. Assuming I do the same amount of SEO, content, links, etc. etc. as YellowPens.com Can I equally climb in search engines, or does the double dash hurt my cause?
You can't exactly find what they are doing for SEO in the background, it may be outsourced to keep their positions in SE's.. So, getting the keyword on domain or doing some SEO stuff only you can't be competitor to them.. better do it on your own way..
Personally I think the double dash looks spammy. I would not recommend this. You should do some further keyword research to see if a 3 word phrase would be more suitable. For example, something like bestyellowpens.com These days most of the good .com's are already taken. You can do just as well with another tld though. Don't be afraid to use a .net or .info. You can get just as good rankings as you would with a .com.