Not very helpful if he's admittedly new and "not good w/ this jailbreaking stuff"...
OP - hold the power and home buttons together to hard reset the device. As it boots up again, hold the volume up buttone (I'm assuming you're on iOS 5 - if not, let me know). This should boot the phone up in safe mode, and your brother can un-install anything that he did recently that may have gotten the phone stuck on the boot logo.
If that doesn't work, do this:
-Attach the phone to your computer, then turn it off
-Hold Power for 3 seconds
-Hold Home AND Power together for 10 seconds
-Release Power, and hold only Home for another 10 - 15 seconds
The phone's screen should go black, and iTunes should recognize that there is a device in DFU mode. From there, click restore in iTunes.
There are a few other things that you can do even if that doesn't work, so let me know. You're definitely not stuck, and it's very fixable!