What can be removed from windows startup?

[Guest mhanbury]

I have the following items in Windows Startup

apersavestar, camera_detect, checkautorun, chgdflnk, connections, cpersavestar, ia_caller_id, npersavestar, poutlook, regnotify, run_bttrayc_e10, stk, tpersavestar, voice command

Does anyone know what each does and if it can be removed?

Also how can you remove the o2 3.6 Active unstable rubbish and put back the 3.5 version!