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I have booted from a Leopard upgrade disk...
Didja notice how long that took?
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I upgraded RAM a few weeks ago
IMO, it'd be good to rule out the new RAM as a possible culprit by swapping out the new for the old as a test.
One possibility that occurs to me is a failing hard disk - have you run a hardware test to check it?
KB
Turn off autoconnection to the wireless network and any similar setting. Looks like it is trying to find the network but can't and is then reverting to the FW connection to look there, etc.
Also startup in Safe mode and see if that improves things.
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To start up into Safe Mode (to "Safe Boot"), do this:
1. Be sure the computer is shut down.
2. Press the power button.
3. Immediately after you hear the startup tone, press and hold the Shift key.
Tip: The Shift key should be held as soon as possible after the startup tone but not before.
4. Release the Shift key when you see the gray Apple and progress indicator (looks like a spinning gear).
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...Just started this week
And you initiated the boot up last week?
Around midnight on Saturday, I hope... 
Really, if you're close enough to an Apple Store to have them take a look, why not? Since booting in Safe Mode didn't improve things, don't you think that points to hardware rather than software?