HowTo? Fixed / Singlespeed conversion from an old bike

first and foremost, you will need a rear mech. fixies = so last year.

That frame so deserves some gears... Pleeeeeeaaaase!!! :(

dude. seriously. sell the frame to someone who can appreciate it properly. don't turn this into yet another stupid newbie 2007 hipster fixie. if you want a fixie, buy a track frame.

He's asking for build advice, we're giving it to him...

That just about says it all. Listen to the wisdom you have been privileged to encounter