I'm not sure if the LAA applet would work on a 32-bit machine with XP. However, the older
NTCore 4Gig Patch used to work. Download that little applet and apply it to the SH4.exe file in your SH4 directory. Check SH4.exe first, by right-clicking on the file and choosing "Properties", and on that first tab "General", in the "Attributes" section, be certain that the "Read-only" tick box is clear (empty). Then run the 4Gig Patch. That might give the game enough breathing room to run properly. Let us know how you do.