I am going to convert my old Giant boulder to a single speed worried about compatibility new to old parts?

the giant boulder is 1998 ish. I would like to convert it into a single speed, I already have a road bike (2010) and would like to upgrade the parts on the road bike and then put the superseded parts onto the old bike. Is this possible with regards to bottom brackets and headset compatibility, as well as fitting road brakes onto a mtb frame? has anyone tried this? i intend to do all of the fitting myself.