HowTo? Fixed / Singlespeed conversion from an old bike

yeah mine was going to be braked and i dont think my knee could skid stop anyways, i was just thinking of it as a quick way to get fixed, if i grab an on one hub will i need new spokes or can i just turn the hub a bit more for the same length ??
ive never built a wheel in my life but my mate reckons he can do it for me

you will need new spokes. use sheldon's wheelbuilding piece, it is not that difficult.

I've got an old Edison cyclocross bike I'd like to make single speed (not fixed, too scared for that). It is currently a triple chainset with bar end shifters, 10 speed cassette. Shoud that be easy to convert?

yes. you need a single speed kit like this which has everything included, you will need a tensioner as i presume it has vertical dropouts and finding a lasting magic gear is a myth. remove the two front rings you don't want, you will likely need some shorter stack chainring bolts, or just cut down the female part of your current chainring bolts. to do this yourself you will need a 5mm allen key, a hacksaw (if cutting down the chainring bolts) and one of these. merely use the spacers with the s/s kit to get correct chainline.