I compared the memory reported by the system with &without the swtich (see attached results). I have 4GB ram, but Isee no big difference.
this is the line added:

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XPProfessional-3GB" /noexecute=optin /fastdetect /3GB

can someone please explain why?SolidworksAdministration