Yeah, when you download a 1.6.4 version of MC through the launcher the Forge installer will detect the install (provided you supply the correct folder) and be ready to go. Make sure you change over to your Forge profile in the launcher too.
Let me know if you have any more questions. For questions about multiple MC profiles see Greevir's video
curse might become the "new place" for mods , but minecraftforum.net is the place most are at and have been. If getting mods from other sites the curse and minecraftforum be careful that they arent malware or mislabeled.