@ sethi_x
if you want to BUY ?? then it should not expire!! because only the trial versions / demo versions are designed to expire after a certain time..
However, if you simply are interested in using CS3 (for educational purposes off course.. ), thats a different issue..
Please get its serial or crack from some site (google it) and have it cracked for you.. if cant find, try CS2 .. you will find keys for it ..