It is 4 gig for 32 bit but that includes the memory on you Video card. That is why the useable amount of memory varies frm user to user on 32 bit, If you are going to have more than 4 Gig if memory and want to use it you must have a 64 bit OS
That is only correct for systems sharing memory with the video card such as notebooks and depends on your Windows version.
The max is 4 GB minus 512 MB for overhead, so you will get 3.5 GB usuable for most Win7 setups not sharing ram with the video card. From the MSDN site:
Version_________________Limit on X86_______Limit on X64
Windows 7 Ultimate__________4 GB______________192 GB Windows 7 Enterprise________4 GB______________192 GB Windows 7 Professional______4 GB______________192 GB Windows 7 Home Premium______4 GB______________16 GB Windows 7 Home Basic________4 GB______________8 GB Windows 7 Starter___________2 GB______________2 GB