Beeping sounds mean somethings up with the hardware. Someone here can tell you what 3 beeps mean - I think its memory, but I'n not sure
EDIT - I AM SURE!
http://docs.info.apple.com/article.html?artnum=58442
I'd check the memory is properly seated, if that doesn't work and you have non-original ram or 2 sticks try removing them or swapping oover.
Also, I'd run Apple Hardware Test from your install dvd - hold option as you start up (it says on the disk), click the icon to the right and run the extended test - report any error codes.
Best of luck