first off, your second hard drive is a slave drive and i don't think you can boot from a slave drive. so, when you select DOS, it says chainloader +1 aand nothing happens? that's weird. how long did you wait? if you waited 5 minutes and nothing happenned, go to Linux, create a boot disk and then use a Windows 98 boot disk to go to DOS and fix your master boot reccord by typing fixmbr.
now to your second question (or first one actually), the username you first use is root which is the administrator user and it is not suggested you use it as a security issue. but for the first time since you probably didn't setup a normal user, login to root with ROOT as username and your password and add a user. there's plenty of help online on how to do that. then logoff the root user and logon o your new username and always use that.
let me know how it went.