QUOTE(miri @ Feb 21 2008, 12:14 PM)

It depends on whether you got your GC through marriage or employment. If through marriage you only have to wait 3 years (so you're good to go) but if it was through employment you need to wait 5 years, so you'll need to wait until 90 days before the 5th anniversary of when your GC was issued.
This is a really helpful tool for calculating when you can apply:
http://www.timeanddate.com/date/dateadd.htmlI believe the sticky at the top of this forum should help fill in all the details.
Also depends on if still married to US Citizen, and how long the US Citizen has been a Citizen. Needs to be continuously married to the US citizen for 3 years, and the US Citizen needs to be a citizen for the 3 years also.
Lastly they could enter on a work visa, and then marry a USC and the 3 years requirement would also apply.
Useful info here:
http://www.uscis.gov/files/article/M-476.pdf