Doesn't look like anyone else has had this issue yet, so i may have just herped and derped and dropped a nuke or something.
Crash log:
Display Spoiler
Mods loaded: 7
ModLoader Beta 1.8.1
mod_Somnia v15 [1.8.1]
mod_BuildCraftCore 2.2.5
mod_BuildCraftBuilders 2.2.5
mod_BuildCraftEnergy 2.2.5
mod_BuildCraftFactory 2.2.5
mod_BuildCraftTransport 2.2.5
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem.
If you wish to report this, please copy this entire text and email it to support@mojang.com.
Please include a description of what you did when the error occured.
--- BEGIN ERROR REPORT 38a78c72 --------
Generated 12/5/11 8:38 PM
Minecraft: Minecraft Beta 1.8.1
OS: Windows Vista (x86) version 6.0
Java: 1.6.0_29, Sun Microsystems Inc.
VM: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.4.2
OpenGL: ATI Radeon HD 4800 Series version 3.3.10600 Compatibility Profile Context, ATI Technologies Inc.
java.io.EOFException: Unexpected end of ZLIB input stream
at java.util.zip.InflaterInputStream.fill(Unknown Source)
at java.util.zip.InflaterInputStream.read(Unknown Source)
at java.util.zip.ZipInputStream.read(Unknown Source)
at java.util.zip.ZipInputStream.closeEntry(Unknown Source)
at java.util.zip.ZipInputStream.getNextEntry(Unknown Source)
at ModLoader.readFromModFolder(ModLoader.java:1174)
at ModLoader.init(ModLoader.java:824)
at ModLoader.AddAllRenderers(ModLoader.java:186)
at aam.<init>(aam.java:61)
at aam.<clinit>(aam.java:10)
at net.minecraft.client.Minecraft.a(SourceFile:259)
at net.minecraft.client.Minecraft.run(SourceFile:629)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 3e0039fa ----------
So, yeah... all I did was take v1.23 out and drop v1.337b in. Boom, crashed.
Normally, I'll find that I can fix the crash myself (mismatched IDs or whatever), but this one is over my head. Anyone know if I can fix it? Until then, I guess I'm going back to v1.23 
[EDIT]
Since the crash log doesn't say anything about IC2, I would just like to point out that REMOVING IC2 from the mods folder fixes the problem... thus, this is caused by IC2.
