I posted here 12 hours ago & my post disappeared. Philippe has covered one area. For the others:
If you recently updated to Quicktime 7.0.4 then see the sticky at the top of this section. QT 7.0.4 is buggy & conflicts with Java.

If that's not the issue, then downld Java using the "Offline" installer: http://www.apple.com/downloads/macos...update142.html
If it refuses to install, then go to your Mac OSX HDD > Library>Receipts folder & remove Java 1.4.2_Update2.pkg & try again to install. See sample here of where to find this package file: Receipts folder sample image

You should also do a safe reboot & repair permissions (restart whilst holding down SHIFT key until you see window saying Safe Booting), then after starting up, open Disk Utility from Utilities folder & repair permissions. Then restart normally & try again opening LW. It's generally recommended to repair permissions after installing softw or updates including OS updates.