Quote from MrBestor
install 64bit java, and create a bat file to launch minecraft with more memory, mc only uses 1gb i believe as default, if your running with 64x64 textures your probably going to need more.
once you install java 64bit make a .bat file with the following line in if you dont know how to make a .bat file google is your friend.
"C:\Program Files\Java\jre6\bin\javaw.exe" -Xmx4096M -Xms4096M -jar "C:\Users\<your user name here>\Desktop\minecraft.exe"
make sure you link the second part to the location of your minecraft.exe it might be in a different loaction to mine.
Thanks so much MrBestor, my MC memory is now almost doubled, but how do I increase it?