Trouble with downloading Itunes 8!!!

Hello,
Im having trouble updating my itunes. i have an old computer that recently crashed but i was about to save it but it knocked me back to the 4.0 version and i just got a new ipod that needs Itunes 8 and everytimei try to download it it will try then say that the installshield script is old and needs a newer version and i tried updating it but it doesnt seen=m to work. Any suggestions?