HMPerson1

Create a zip archive containing the config file at .minecraft/configs/forge.cfg Attach that zip to a post, then delete the config file.

Seems like an NEI bug. Go poke at ChickenBones.

Download them to .minecraft/libs

Software Update never has had, and probably never will have an update to Java. Apparently Oracle made Java 7 updates only available to OS X 10.7.3 (Lion). Go yell at the author of whatever mod you installed not to use Java 7 then. [spoiler=More Info]According to this, as of Java 7u6 only OS X 10.7.3+ is supported. Java 7u5 should work on OS X 10.6.8+. However, older archived versions of Java are unavailable for download to the public. So...blame the mod author.

Try downloading the files mentioned in the logs manually.

Update Java. Before you say anything about Java 7 being not available for Mac: Look here.

java.lang.NoClassDefFoundError: com/google/common/collect/Multimap That specific error is in the EAQ.

Which mod specifically were you trying to install?

You probably have 1.4.7 mods in your mods folder. Make sure all your mods are up-to-date.

Download the files to .minecraft/libs

Update Forge.

NEVER install ModLoader with Minecraft Forge. Bad things will happen.

Post the WHOLE logs.

How to install

Your world may be corrupt. Make a new one.

Double check you have the same client and server configs.

Delete META-INF

Make sure you're running the latest version of Forge; this bug was fixed ages ago.

What launcher are you using?

You probably have another mod that's doing something improperly.

Read the logs or the EAQ.

You forgot to install a mod that Galacticraft needs. Check their installation instructions again.

[lmgtfy]BukkitForge[/lmgtfy]

Delete all ForgeModLoader-client-#.log files, run Minecraft, let it crash, THEN post the new log files.