My husband and I are planning to invite my sister for a visitor's visa. My sister is an irregular 4th year college student and by the next school year in June 2008 she has no subject to be taken up in college instead all her remaining subjects in order to graduate is in the second semester. Is a certification from her school stating that she has still to enroll in the second semester is valid enough as a reason that she will come back home?

I am still a greencard holder, do you think it will affect my status right now if i will invite her in the US? Do she needs to show that she has enough funds to support her stay although we want to shoulder all her expenses while staying here? Any help will be highly appreciated. Thanks...

A visitor's visa is issued on the merits of the applicant (your sister not you). An invitation letter I am almost certain rarely influences a decision..

Your status is not affected

This is not a K-3 visa question it has more to do with " Bringing family members of Permanent Residents to America"

http://www.visajourney.com/forums/index.php?showforum=112

the United States Embassy web site in Manila has complete answers to all your question.
http://manila.usembassy.gov/wwwh3024.html
Is is simple and straight forward and is right!
Under the consular & Visa section
click NON-immigrant
then on the left scroll down to visa classification
under that click on visitor (B1/B2)
easy from there
Good luck