1  Download The Creep Mod (looks like you have already done this :P)
2. Download the latest Minecraft Forge installer for your version of minecraft from:
   http://files.minecraftforge.net/
3. Choose the 'Install client' option on the Forge installer and install it.
4. Access your .minecraft folder (there are many tutorials on this if you don't know how)
5. Navigate to the 'mods' folder, creating it if it doesn't exist.
6. Copy 'The Creep Mod Vx.x.xx_x.x.x' from your download destination to the 'mods' folder.
7. Launch Minecraft using the new 'Forge' profile.
8. ???
9. PROFIT!!!

IF YOU ARE EXPERIENCING ERRORS:
1. Disable all your mods, and re-enable them one by one, to see if a mod is causing you grief.
2. Check that you don't have anything else in your <version>.jar file, as this will likely
   cause issues.
3. Ask me on The Creep thread at www.minecraftforum.net, I may have a solution for you :3

INSTALLING OTHER MODS:
This is a Forge mod, so (barring and Block, Item or Biome ID conflicts) it should work well 
with other Forge mods for the most part. If you have any ID conflicts, just go into
.minecraft/config/TheCreep.cfg and change the numbers in that file.