I have a MBP w/ 2.16GHz Intel Core Duo running 10.5.8.

I purchased Limewire PRO 5.

I didn't have any older/other versions of Limewire installed.

The installation went along fine, and the app was installed in the applications folder along with a link on the desktop.

When I try to run the app it won't run. It doesn't show to be running anything in the system and doesn't report any problems.

I tried reinstalling, running it from the link and the app in the applications folder. nada.

It never gets to a point where it asks for an activation key or anything else.

Any ideas?

1. Check under Apple icon top left of screen for Software Update ... see if there are any system updates waiting.

2. I'd suggest you do a Safe Boot & Repair permissions. Hold down SHIFT key whilst your computer is booting until you see the apple icon. Then log in. Then open Disk Utility, select the OSX drive on left & choose Repair Permissions. Then reboot normally & try LW again.
Repair permissions should normally be done after any system updates, however might be wise after any adobe updates also such as flash.

3. An idea might be to check if the problem is account related. Set up a temporary test account & see if LW runs from there: Setting up a Test Account in OSX (click on link). You can easily delete this account later, doing such removes all support folders & files for the second account.

4. One option that usually works is one which is harder work. It means reinstalling MacOSX from the installation disks. This means a clean install which deletes all other data on the drive. Obviously you would need to backup all personal files, any installer programs downloaded, etc. Obviously this option is the less inviting one, but always seems to fix the issue. I believe the issue is an issue with the original java installation.

Well I already had my s/w up to date, so that was easy enough.

I did a disk repair, but that didn't resolve the problem

I created a test account, but had the same problem. The LW icon starts to appear in the dock and then disappears.

I don't want to reinstall the os and then reinstall everything, too much risk for not enough benefit. Perhaps I'll upgrade the os and see if that fixes it.

You did say 'intel' macbook pro right, otherwise if not an intel mac it won't run on OSX 10.5
You need Java 1.6 (Java 6) to use LW 5. The way to check is go to the Utilities folder, open Java Preferences. Now, if you do not see this version of Java you cannot use LW 5. However you will probably see multiple versions of Java listed in the order of preference of use. Put Java 1.6 (Java 6) at the top of the list. Play around with the order & see if this helps.

I'd hate to think you'd have to use LW 4 instead. But this might be an option.

It's an intel mbp. In java preferences it shows j2se 5.0 32 bit under the general tab. I'm guessing this means java 5.0. So how do I get 6.0? Or is J2SE something different.

If there is no Java 6, then unfortunately you won't be able to use LW 5. Unless you upgrade your OSX to Snow Leopard 10.6
If Java 6 is not listed in Java preferences, it means your computer is not compatible with the 64-bit Leopard version of it. Snow Leopard has a 32 bit version of Java 6. Blame mac for that.

Your options if you don't upgrade to Snow Leopard are to use an earlier version of LW Pro. Go to your LW Pro download page at their site & see if any earlier versions are shown. If not, let me know.