You are using 32-bit Windows Vista, and are limited to using 32-bit Java. This means you can't give enough memory to play most of the 1.6.4 FTB packs, which require you to give them 2+ GB of RAM. The only 1.6.4 FTB pack designed to be played on 32-bit systems is FTB Lite 2.
Additionally, your Java is out of date; you can find the latest version of Java here:
http://www.oracle.com/technetwork/java/javase/downloads/jre7-downloads-1880261.html
You will need to update Java to play FTB Lite 2 properly.
And unfortunately, the only real solution to your problem would be to get a new computer with a 64-bit OS and preferably more RAM (8 GB total is a minimum in my eyes for new computers today).
