A total noob questions, please help a newbie

I am a heavy noob at SEO.
All I know how to do is to post content and install wordpress SEO plugins.

I've been spammed with email about this software "Niche Finder" and it looked awesome but interesting fact is that I don't see you guys talking about it.
Watch youtube video with id m1PZNIkCv30 (youtube v=m1PZNIkCv30) to see what I am talking about.

So is it good or is it some scam?

One guy recommends this software in another new topic:
Xrumer
SEnuke
Scrapebox
BMD
Market Samurai

I am thinking of investing like 100$ into software - I just don't have real income, 80% of my income is from my salary job and the other 20% are from other IT stuff, but not IM.
What I think I need the most is a niche/good keywords/ finder so I optimize for them.
But I actually don't know what Xrumer, SEnuke, Scrapebox, Samurai are capable of / are used for. Can you please explain in 1-2 sentances?

I am thinking of building an adsense site about wallpapers.
Can you give me any tips?
Like what payed services can I use for like 20$ that will have the biggest effect in this budget?

Good to start out small with scrapebox and some proxies if you have low startup cash and get a feel for it. Dont buy any other stuff till u fully know what it is, how u can use it and if you need it. Scrapebox mainly does blog commenting but has lots of tools and uses such as keyword scraper, proxy harvester, link checking.
The other ones I don't own so best someone else describe but some have quite a high monthly cost so if you are not putting them to good use will just drain your money

Philipuk1983 thank you so much for your reply.
It was very meanfull.

The thing is - I want to know about what keyword to SEO.
When you say scrapebox can be used for "blog commenting, keyword scraper, proxy harvester, link checking":
1. blog commenting - doesnt this got fucked up by resent google updates?;
2. keyword scraper - idk if this means that it finds good keywords;
3. proxy harvester - in my translation this means that it gather's proxies that can be used, but I have no idea what to sue them for;
4. link checking - when you say link checking... it only comes to my mind "backlinks checker" and "page rank checker";

So as you see I amkinda the noober of the noobs, so even if the best advice you could gave me was to start with scrapebox - I have no idea what to use it for.

Also I want to buy some backlinks/bookmarks/whatever and I can't tell what's good and what's not.

A week before or maybe two I read a "case study" where one dude linked up to services he bought and got to #1 for his keyword. But I am kind of not sure if he doesn't adv. them or something.

I would go with UltimateDemon instead of Bookmarking Demon.