Thanks Zero for your reply!
Don't you mean that Forge has a built in replacement for ModLoader? Well, I know that it shouldn't be compatible with MLMP and I believe all of you, but the strange thing is that it works if you just install MLMP before Forge... Now, that this normally shouldn't work, I think that there are any disadvantages and that I better do not use MLMP mods until they are ported to Forge... Well, I'm just going to reinstall Forge without ModLoader, ModLoaderMP and AudioMod and I hope that it will work... But it's strange, that it works...
EDIT: I've just red that Forge and MLMP are compatible with each other, but only in SSP. In SMP they'll conflict. I won't use ModLoaderMP mods now, I'll stick with Forge. Goodbye MLMP, hello Forge!
EDIT 2: I just decided stick with 1.2.5 until 1.4 is out and I use ModLoaderMP with Forge for SSP and for SMP only Forge. That does not conflict and works fine. Are there any disadvantages to use MLMP and Forge in SSP?