i just got a set of summit headers for my 1995 chevy truck, a sticker on them says not a high temp finish. can i put them on without any harm or do i need to have them coated, if so are ther any do-it yourself coating?

They are probably shipped with a "packing coating" which is very thin, and will not stand up to operating temps. You will probably want to either sand/steel wool ALL of this coating off down to the bare metal and them apply a good coating like VHT High Temp or a similar header paint. These high heat coatings come in a bunch of colors and types.