You only have 32bit windows and therefore the FTB launcher will only use a maximum of 1gb of ram. I would expect you will need more than that to use the sphax pack. Stick with default or try, if available a 32x version. How much memory does your system have? If you get the 64bit version of windows you will be able to use the 64bit java and you will be able to allocate more ram to FTB.