keyboards, mice and speakers should work with windows 7. in fact i had a keyboard from 1985 hooked up to my pc and it worked fine! the only thing which might not work is any special software which was included. typically if there is a driver update required you could get it from the manufacturers website. if there are no updated drivers available, and the included drivers will not work then you could just go without them and use the windows-standard drivers. the only things which wouldnt work are any special multimedia keys on keyboards and extra buttons on mice. other than that, usually things work ok.
if you already have the keyboard, mouse and speakers in your possession (from an existing build) there is no harm in connecting them up to your new pc. if they work they work, if they don't you could get newer ones with no harm done. although, they should work.