Here's what I found out about Green Cards (Permanent Resident) through marriage from wikipedia:
http://en.wikipedia.org/wiki/United_States_Permanent_Resident_Card
"...persons who are eligible and properly apply for permanent residence based on a recent marriage or as an investor are granted permanent residence on a conditional basis for two years following an initial interview with an agent from USCIS.
...when this two year conditional period is over, the permanent residence automatically expires and the applicant is subject to deportation and removal. To avoid this, 90 days or less before the conditional residence expires, the applicant has to file Form i-751 (if permanent residence was obtained through marriage) or i-829 (if conditional residence was obtained as an investor) with USCIS to have the conditions removed. Once the application is received, permanent residence is extended for one year intervals until the request to remove conditions is approved or denied.
General, as well as specific supporting evidence that the basis on which the applicant obtained conditional permanent residence was not fraudulent is required by USCIS to be included with the application. A followup face to face interview (i-751, removal of conditions) with an immigration inspector is sometimes required but usually waived if the evidence is sufficient. This is to ensure that the marriage was in good faith and not one of fraudulent means with a sole intention of obtaining a Green Card. Both husband and wife must attend both interviews under most circumstances. The applicant receives an i-551 stamp in their foreign passport upon approval of their case. The applicant is then free from the conditional requirement once the application is approved. The applicant's new 10-year permanent resident card arrives via mail to their residence several weeks to several months later and replaces their old 2 year conditional card."