2 Easy Questions

I have the new iMac...

1. How do I stop the sound it makes when I turn it on? (it does this even though when I turn it off, sound is off, and I have speakers plugged into the headphone jack that are off...)

2. How do I keep the screen from dimming ever 2 minutes?

1)... You can't. Well you can if you MUTE the Mac prior to shutdown.
It's a system test to make sure all is well.

2) System Prefs >>> Energy Saver. Adjust as you'd like.

Congrats on the Mac!!!!

You could use this:

http://macupdate.com/info.php/id/16425

There are ways of stopping the startup chime, search these forums and you'll find a way within a few minutes, I've seen a fair few threads about it.

Thanks for the help, but I can't seem to stop the dimming. I can adjust when the display turns off, but I can't seem to stop it from dimming after about two minutes...

System Prefs >>> Energy Saver >>> Options.

UN-Check "Auto Dim screen before sleep".
Do it in BOTH "On Power Adapter" and "On Battery"

take a look at this thread:
http://www.mac-forums.com/forums/showthread.php?t=63286&highlight=screen+dimming

I have this with my macbook pro and have since gotten used to it.