I am on a H4 visa and my husband is on a H1b visa. His I-140 had been approved and his company will file for it in Feb 2012. So he will get 3 years of extension. His green-card process is in EB3 category right now and they will convert it to EB2 by the end of 2012. I want to do my MS (will begin in 2012) and am thinking of converting to F1. After I complete my course in 2014, I will either go back to H4 (if I don't get a job) or H1b status. My questions are:

1) Will there be any sort of delay or problems with his green-card process due to changes in my visa?
2) If I travel to India will it be difficult for me to re-enter US as I will need to get my visa stamped?
3) What are the other possible problems that might occur w.r.t green-card?

We have been through similar situation. I have I-140 approved and still waiting for visa numbers to apply for I-485.My wife converted her visa from H4 to F1 to H1. My wife got her F1 stamping with out any problems last August. We recently converted it to H1.
I do not see any issue with your GC.
But Visa stamp is getting tougher these days. But to your advantage, if you have already completed 1 or 2 semester and paid your fees,there should be no problem.
But on other note you can take advantage of in-state fees on H4 visa.