port of entry

when you go through port of entry in the states and present your package/imigrant visa (from the embassy in the UK ) are you issued with a temporary green card straight away and will that enable you to come and go , in and out, of the states, or do you have to stay in the states from that time until your permanant green card is issued? Please if you know answer back
The reason behind this question is because I intend to live in the states but am not ready yet to go for good but need to visit for a week very soon and want to present my papers then

when you go through port of entry in the states and present your package/imigrant visa (from the embassy in the UK ) are you issued with a temporary green card straight away and will that enable you to come and go , in and out, of the states, or do you have to stay in the states from that time until your permanant green card is issued? Please if you know answer back
The reason behind this question is because I intend to live in the states but am not ready yet to go for good but need to visit for a week very soon and want to present my papers then

What Port of Entry you are planning to use?
Are you comming from Canada/Mexico?

we are coming from the UK

It will be treated as LPR. Any time if you stay out of US for more then 6 months then your status automatically cencelled. unless you apply for permission from the INS.

When you migrate to the U.S., your passport is stamped at the port of entry with a "evidence of permanant residence" stamp, valid for one year. This is as good as the "green card" you will get in the mail later on.

You can leave the U.S. for up to 12 months and maintain your permanent residence or 2 years if you file the correct form.

If you want citizenship later on, you should not leave for 180 days or longer (except in special circumstances like serving in the armed forces), at any one time.