seo for page vs. same print page

[coders]

A website page which I will be doing seo is like:
[www...] dot abc dot com?nid=123 and its print page is like:
[www...] dot abc dot com?nid=123&st=print

I just wanted to confirm that I have to do seo for the first one and not for the second one. Am I correct?

Then, as these pages are live running, they have actually the same content so can duplicacy issues arise?
Should I block them in robots.txt?

What to do for these print pages? Just leave them as it is and do not submit them in sitemap.xml?

Please clarify my doubts !
Thanks

[coders]

Appreciate all ansers !
Anybody please

[phranque]

welcome to WebmasterWorld [webmasterworld.com], coders!

you should probably put rel="nofollow" on your links to the print pages as well as specifying NOINDEX for the print pages with the ROBOTS meta tag.

if that is not an option you could block with robots.txt but don't do both or the bots won't see the noindex.

[coders]

Thanks phranque for your answer!