Admin Password no longer works

So, I go to log into my account this morning on my iMac, and it tells me my password isn't valid.

Unfortunately, my login is the admin account.

At the moment, I have no access to my files, and cannot do anything that involves admin privleges, such as repairing permissions, etc.

Oh, and I can't find my iMac instasllation disc. Or my Tiger disc.

I'm pretty much boned until I do find them.

Once I do find them, will I be able to reset my admin password without a valid admin password?

My suspicion is that something got corrupted somewhere - possibly permissions. Anyone run into this before?

Also I don't suspect anyone of changing the password, as the only two people with access are me and my wife. And my wife doesn't mess around with system prefs.

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iMac Intel Core2 Duo 2.33gHz - 24in. - the white one, not the aluminum one.