Should not need to delete anything if do an
Archive Install. All it does is install the new system folder, copy all or almost all preferences & support files from the old system folder to the new one. So after installing, you can then delete the old system folder (which will take up perhaps 10-20 GB.) But double-check your old personal account folder first just to be sure everything was copied to the new one.
You should repair permissions however after doing this.
This is the best alternative I can think of. Otherwise LW will simply not run on your machine. There may be other problems your computer has you don't realise.
Downside of doing this: Some applications such as final cut pro might need to be re-serialised. But most apps should be fine. You will need to download the update packages for OSX after reinstalling the system. However, Mac packages all the system updates into a single installer, inclusive of all other updates so no need to download separate 10.5.2 & 10.5.3, etc. updates.
* Oh .. when doing the Archive Install, click the
options button to be sure you are installing only what you wish to install. You can uncheck most of the language packages for example to save hard disk space.
Happy to help where I can.