So I found the old mountain bike that I got for my 12th birthday (12 years ago!!) in my attic.... I want to turn it into a SS but I do not know what to do about the wheels... it obviously had MTB wheels on it, and it has cantilever brakes.... so a 27" isnt going to work out (tried it today...) anyhow, WTF??? What are my options here for wheels/ brakes.... any info would be RADICAL!!! Thnx

You could take off the old cluster and screw on a single speed freewheel cog. Then re-space and re-dish the rear wheel. There are lots of articles on the internet about how to do this.

I'm also currently building up a SS MTB and was planning on using this method.

Keep the cantis!
Also look for slick 26" tires. Not hard to come by at all.

I've got a near new pair of panaracer ribmo's laying around. 26x1.75. semi slick/Light tread. PM me if you are interested.

As said before, just use spacers and a single cog. Surly makes a singlespeed kit as do a few others. You may need a chain tensioner if you don't find the perfect gear ratio.

Heres a good place to start:
https://www.mtbr.com/ssfaqcrx.aspx

The wheels that were on it are no good.... so what should I buy at the LBS to throw on it? Anything that can just go right on and be able to ride?