This post is intended to people like me who won’t install Leopard on an empty, clean Hard Drive.
I won’t have the courage to back up my 80 gigs + iTunes library or my movies and documents, so all I’m going to do is preparing my Mac to be updated to Leopard from Tiger.

It is Highly recommended to backup all of your datas before upgrading to Leopard anyways, there is a great article at Apple’s website on How to back up and restore your files.

Here are some advices I have to give and some others I collected here and there on some Mac sites.

1. Before installing Leopard, check your startup drive for damage, and repair it if necessary. The easiest way to do this is to boot from the OS X Install DVD and run Disk Utility (from the Installer menu). Click the First Aid tab, select your hard drive in the drive/volume list, and click “Repair Disk.”
2. Make sure all devices are synchronized prior to updating If you use mobile devices that synchronize with iSync or another application, make sure that the data is updated on the Mac before upgrading to Mac OS X 10.5. Some applications, iSync (the Leopard release) included, will not seamlessly adopt data synchronization for existing devices.In other words, iSync in particular, will either re-initialize the device from the data on the computer (losing any changes made on the device since the last synchronization) or merge the two data sets, creating duplicates.Making sure that the latest data is on the computer side will allow you to re-initialize your device without losing anything.
3. Disconnect all external devices, update firmware This may seem like overkill, but disconnecting all external USB and FireWire devices before applying Mac OS X 10.5 can save you from some serious but rare problems including drive corruption/failure and system startup issues caused by problematic devices.Disconnecting all FireWire devices before updating is especially important, and is a procedure we’ve recommended several times in the past. Apple even recommended this procedure for some incremental Mac OS X updates, stating:”If you have a third-party FireWire hard drive connected, turn it off and disconnect it before installing this update. Reconnect it and turn it back on after installation is complete and you’ve restarted.”This includes iPods.After successfully installing Mac OS X 10.5, attach each device individually and check for issues.

   Also, make sure that you are using the latest firmware, usually available from the manufacturer’s Web site. Updating the firmware can resolve a host of mounting and access issues that can occur under Mac OS X 10.5.

4. Try to remove as many third party widgets as you can, third-party Dashboard widgets live in ~/Library/Widgets.
5. In /Library, /Library/Application Support, ~/Library, and ~/Library/Application Support, look for folder names matching applications you no longer use, and delete them.
6. Your /Library and ~/Library folders may contain other folders that store components of third-party utilities. Look in Application Enhancers, Bundles, Contextual Menu Items, InputManagers, and PreferencePanes for any system enhancements you no longer use, and drag them to the Trash.
7. Applications use cache files to increase their speed and efficiency, and rebuild them automatically if necessary, so you can delete them safely:
   1. The contents of /Library/Caches and ~/Library/Caches, can sometimes occupy hundreds of megabytes of valuable disk space. Drag these files to the Trash.
   2. You can empty Safari’s cache by choosing Safari -> Empty Cache (Command-Option-E).
   3. Safari stores favicons (those tiny icons that appear next to a site’s URL in the address bar) separately from its main cache. To remove them, quit Safari and drag the folder ~/Library/Safari/Icons to the Trash
8. Software that requires some component to be running in the background all the time may install folders in /Library/StartupItems. In most cases, you should leave this folder alone, but if you see anything there from software you’re sure you don’t use, delete it.
9. Your ~/Documents folder is a likely place for unneeded files (by ~/Documents, I mean look in your user folder for a Documents folder). Skim the contents of this folder and its subfolders, looking for documents and application support files you no longer need, and drag such items to the Trash.
10. If you frequently download files from Web sites or receive large e-mail attachments, look in your Web Downloads folder (Safari uses your Desktop folder by default) and your Mail Downloads folder (Mail uses ~/Library/Mail Downloads by default) for old, unneeded files you can delete.
11. Look in /Applications (and /Applications/Utilities) for any software you’ve installed over the past year but never use. (Expired demo software, anyone?) Resist the temptation to delete Apple software that came with Mac OS X, though; although new versions of some of it may be included with your Leopard upgrade, I can’t guarantee that all of them will.
12. Kernel extensions (files with names ending in .kext) add low-level functionality to Mac OS X. Examples include hardware drivers (for devices such as mice, trackballs, and audio interfaces), encryption tools, screen-capture software, and Parallels Desktop. These files are stored in either /Library/Extensions or /System/Library/Extensions, and you should not delete them manually unless the developer’s uninstallation instructions tell you to do so, or you are certain they must go and you have no other option.

Find more advices here.

Posted in 3rd Party Software, Mac OS X, Macintosh Tips & Help