I really don't understand what you are trying to say
1-gone past the 30 day trial
2-given Adobe CS4 by a friend
3-serial number for CS4 which i have
Do you have the trial version, or a purchased version?
These discussions are for CS3 but the ideas MAY help
License not working for any CS3 product http://kb2.adobe.com/cps/405/kb405970.html
or Activation Error http://kb2.adobe.com/cps/855/cpsid_85519.html
or Configuration Error http://kb2.adobe.com/cps/827/cpsid_82744.html
But then they want the serial number for something I don't have
Your "friend" gave you an upgrade version. He/she also needs to give you the older version. That has the other serial number.
the serial number for CS4 which i have and is valid.
This may also not work if your friend upgraded to CS5 by using the CS4 license.