Click Options. Change the RAM Maximum to something more generous. 4GB or more is ideal. 2GB minimum
On the Mod Pack tab, The pack you want is: Monster (v1.1.0)
http://feed-the-beast.com and download their launcher. I always use the JAR version but you can use the exe if you like
See world map here:
Read on if the above was not clear.
To get the 64-bit version, go here: http://java.com/en/download/manual.jsp
Change the version from Recommended, to 1.1.0 (in the drop-down next to the private packs button)
The pack might appear to stall after the download is complete. This is normal. Just be patient.