zedkar is right about the current requirement of 64bit to use the 1.6.4 packs
as is. Which is why FTBLite2 was created for slower systems. The reason 64bit is required is because of the hard limit to memory that Java puts on Java programs of 1GB. The newer packs work best on 2+GB.
If you are not trying to run the 1.6.4 mod packs or cannot even get the launcher to start then please follow this recommended setup
guide carefully and precisely. After following the guide if you are still experiencing problems please post a console log to pastebin.com by clicking on the 'Paste my log to pastebin.com' button on the launcher. This will create a link to where your log is saved on pastebin. Provide us the link so we can see your log. If the button times out or it does not create a link, please copy the log yourself to pastebin.com and provide the link it gives you. Be sure to create a free account with pastebin.com so your log does not get deleted in 24hours. Look
here for more info.