Err, drag the application or application folder to the trash.

It's not like Windows where it needs to uninstall loads of DLLs and the like. If there's files stored anywhere else, the ReadMe file in the application folder usually tells you where all the files are for uninstalling.
If it's a utility that needs to install extensions, there's usually an Uninstall app somewhere in the application folder, Microoft Office does this.

A great tool is InstallerObserver; it tracks what happens on your HD or on your system folder. Download for free:
http://www.tucows.com/preview/207015

For quick removal, have the file/s you want to delete selected and use command/ delete.
You will notice that the trash icon is overflowing. Go to the special menu
choose empty trash. A dialog will appear asking you if you want to remove these items. Click OK.
If you want to avoid the dialog, hold the option key while choosing empty trash.

the usual way...
Mouse over and click on the app/doc you want to erase/uninstall
DragN´Drop to Trash
Menu/Special/Empty Trash
Click OK en the ¨Are you sure...¨ dialog box
And forget about it.

Beware of invisible files, though. Normally, Macintosh applications don't install invisibles. However, some apps/installers do, especially if they want to hide registry or trial version expiry information. Dangerous in this regard are especially Adobe trial versions, Ready!Set!Go! trial versions, Z-Write, NisusWriter, etc. Also TechTool Pro 3 installs all kinds of invisibles.

If you suspect that an installer might install invisibles just monitor, with InstallerObserver, the entire HD. If you do not expect that an installer might install invisibles it is sufficient to monitor the system folder. Everything an installer does not put into the system folder it puts into an application folder which you can just drag into the trash.

Some installers offer uninstall possibilities. If this is the case, the installer offers this option as an alternative to "Easy Install" and "Custom Install"; it then also offers "Uninstall". However, an Uninstaller normally does not uninstall Preferences out of the Preferences folder in the System Folder. Preferences are normally not installed by an installer but by the application itself during the first start up.

Some apps, especially Adobe, install information into the document folder of the HD. Uninstallers normally do not uninstall stuff installed into the document folder. You have to drag the stuff into trash by yourself.

Some installers install locked files. In order to trash those files you have to unlock them first, either by via the "Information" menu or, easier, with apps like EmptyTrashFast.

In some very rare cases, an installer makes amendments to the system itself. In this case YOU HAVE TO USE the offered Uninstaller, because you cannot see the change. Otherwise the system remains changed which can be fatal. Try to avoid installing apps that mess with the system.

Yes, but there are not that many invisibles in Mac OS 9.

If you installed something before using InstallerObserver and suspect that there are secret files like from trial versions on your HD there is a trick you can try:

Use PlusOptimizer from DiskWarrior. Most of the secret files are not moveable by PlusOptimizer so that PlusOptimizer will give you a warning saying PlusOptimizer did not move this and that file. Often these files are remnants of trial version files or other registration files.

Was there not also a Mac app called InstallerSpy. You didn't actually have to run the installer, it read the installer script and told you what files were installed where.

Yep, I still have it on my MDD. I'll try to find the original on locked media ....

Found this:
http://www.filesearching.com/cgi-bin/s?q=installer-spy&t=f&d=&l=en
Will check; maybe this is what you mean.

Thank gppdness for DiskTracker .... http://www.megaupload.com/?d=I4HR8CGL

The InstallerSpy helps me too, just what I was looking for. InstallerSpy says it needs version 4.0 or greater of the Installer to work. I don't have that, so I'm assuming this app won't work for System 7.6.1.

Mmm, that version of InstallerSpy works with Installer v4, but it also works with all the earlier versions too. I have earlier versions of InstallerSpy that work only with Installer v3 and earlier.

In case that there is no earlier version of InstallerSpy here is 68 K version of InstallerObserver:
http://www.info-mac.org/viewtopic.php?f=111&t=3139&p=3140&hilit=installe...

Don't forget the Preferences file, a oft-visible file that is created when an application starts. It's not especially space-consuming, though, so you may just want to forget about it.