You have someone else go online on a different computer or you go online on a different computer, download the installation file for ZoneAlarm and then burn the installation file to a CD-R or a CD-RW. Take the CD-R or CD-RW to your computer and reinstall the ZoneAlarm.
Anyway, why can't you go online? I suppose that ZoneAlarm is preventing you from connecting right? If so, there is a way where you can open up ZoneAlarm and go to the place where it lists the programs and find your ISP and then make sure that ZoneAlarm is set to allow it to connect to the Internet. I don't have ZoneAlarm anymore so I can't give you specific instructions as I don't remember what everything is like in ZoneAlarm. Also, I'm pretty sure there is a way to manually add programs to the list in ZoneAlarm and you may have to manually add your ISP's program so that you can connect to the Internet. If you can get that working then you should be able to go online and download ZoneAlarm. Also, another option would be to uninstall ZoneAlarm and see if that lets you go online. This is of course assuming that the reason you can't go online is because ZoneAlarm is preventing you from going online. Hope this helps!