QUOTE(YuAndDan @ Jun 17 2007, 12:09 PM)

An LPR can apply for citizenship 90 days before their third anniversary of obtaining LPR status if married to a US citizen, or 90 days before their 5th anniversary if not married to a US Citizen. (There are residency conditions also like not being out of the country for periods no longer than 6 months, and live in the USA 18 months of the 3 years OR (6 months and 30 months if not married to a USC))
LPR status begins at the issue date of the 2 year conditional card.
So No you cannot apply right away, you need to wait 33 months (Married to USC) or 57 months (Not married to USC) before applying for citizenship, or be nearly 1 year into the 10 year card.
SEE:
http://www.uscis.gov/files/article/M-476.pdfYou will have to apply to "remove conditions'" 90 days prior to the 2 year expiration date of your "temporary" GC also before you can apply for USC.
Strange as you'd think you could just wait for the 3 years and go for USC instead.
I guess USCIS just wants to make more $s on application fees.
Can't really see what the functional part is!
Some people don't really care about getting their USC tho!