Is there a way to when you received new mail , instead of opening you mail client , to just display a box on the screen with the headers of the email or just the subject ?

not built into litestep, no. try http://download.com.com/3120-2001-0-1-0.html?qt=email%2Bpop%2Bcheck&li=49 for a few free third-party options.

I use The Bat! as my email client and it has an email ticker scrolling the headers of received email.
Naturally I thought it was cool, so I've been looking into adding the support to LSMail as well, but for pop3 one needs to dl the mail and parse for the header, so it's a feature that would appear far away into the future... (it wouldn't be far from a complete client once that is done)

I could have sworn that you could request e-mail headers from a pop3 server without downloading the actual e-mail?.?

I think IMAP has that feature, but I've only seen RETR (get full) and TOP (get first nr of lines) in pop3 documents.

TOP gives you the message headers plus n lines of the message. So TOP 0 should just give you the headers.