Building a transformer

I decided to have a look into switch mode psu's in the end, and furthermore building my own transformers seems far more complicated tham I originally anticipated. So i've looked into the switched mode psu's, and they seem fairly straightforward (famous last words), further to that i'm bugging the local computer store for any and all busted computer power supplies - and i'm not even charging them for 'disposal'. That way I can gather many transformers at no cost to me and experiment away to my hearts content. I figure if I need a lot of power I can run several of these transformers in series or parallel.

Mark