Well, I want to create my own stairs =)

How do I actually do that?

 

Copying everything out of the BlockStairs.java and rewrite it?

Extend the BlockStairs.java?

Extending BlockStairs would be easiest.

Well... doesn't matter if i'm trying to extend or copying it, I always getting kicked to the com.google.common.eventbus.EventBus class in eclipse, means my minecraft doesn't even start correctly ...

Post a log - the ForgeModLoader log.

Directly out of eclipse:

2012-09-28 11:23:03 [iNFO] [ForgeModLoader] Forge Mod Loader version 3.0.165.344 for Minecraft client:1.3.2, server:1.3.2 loading
2012-09-28 11:23:04 [iNFO] [sTDOUT] 27 achievements
2012-09-28 11:23:04 [iNFO] [sTDOUT] 195 recipes
2012-09-28 11:23:04 [iNFO] [sTDOUT] Setting user: Player509, -
2012-09-28 11:23:04 [iNFO] [sTDERR] Client asked for parameter: server
2012-09-28 11:23:04 [iNFO] [sTDOUT] LWJGL Version: 2.4.2
2012-09-28 11:23:05 [iNFO] [ForgeModLoader] Attempting early MinecraftForge initialization
2012-09-28 11:23:05 [iNFO] [ForgeModLoader] Completed early MinecraftForge initialization
2012-09-28 11:23:05 [iNFO] [ForgeModLoader] Searching C:\Users\Du5tin\Desktop\AVD\6\MCP\1.3.2\jars\mods for mods
2012-09-28 11:23:05 [iNFO] [ForgeModLoader] No mcmod.info file found in directory bin
2012-09-28 11:23:05 [iNFO] [ForgeModLoader] The mod container minecraft.jar appears to be missing an mcmod.info file
2012-09-28 11:23:06 [iNFO] [ForgeModLoader] Forge Mod Loader has identified 3 mods to load

"I always getting kicked to the com.google.common.eventbus.EventBus class in eclipse, means my minecraft doesn't even start correctly ..."

 

I see no mention of that in the above log. Explain a bit more clearly what happens?

I fixxed the problem now, by looking over all assigned block id's again, and mentioned... that forge doesn't show up an error in eclipse if 2 blocks have the same id?

Minecraft itself will throw an exception if 2 blocks have the same ID.  Forge does not change that at all as it is quite effective.  You can blame Eclipse for catching the exception.