Increasing the amount of application memory at the expense of system memory isn't likely to address memory problems in Windows XP 32 bit. It isn't the general application paged pool memory that runs out in most cases. Applications that have a Graphical User Interface must allocate GDI OBJECTS and USER OBJECTS (GDI=Graphics Device Interface). There are limits on the number of such objects that may be created by any single process and there is also an overall per session limit. Per session means a session desktop for a logged on user.
SketchUp makes heavy use of such objects. Other applications such as Windows Explorer and Internet Explorer are also very heavy users. When the maximum limit for User Object or GDI Objects is approached the system will begin to degrade. It doesn't usually crash but certain functions such as the clipboard and right-click context menus will stop working.
You can see here how many objects are being allocated by various processes:
http://ixian.ca/pics8/process_exp.gif
The only way to recover the ram used by these objects is to close the apps that are using the space available. Internet explorer is particularly bad in this respect. Firefox isn't any better. The best browser that I have tested is Opera. It uses far fewer objects when multiple tabs are open.
Existing allocated GDI and USER objects will not be deallocated until all instances of an application are closed. The situation becomes even worse if Terminal Services is running. Then the GDI ram is allocated from the unpaged system pool instead of the general application paged pool and the number of allowable objects drops dramatically. In fact, if Terminal Services is running then using the Large Address switch on XP will make the situation much worse.
Bottom line: There is no benefit to using the Large address switch on Windows XP 32 bit and that probably includes the 64 bit version although I am not certain of that.
References:
Process explorer is a part of the Sysinternals Suite available here:
http://technet.microsoft.com/en-us/sysinternals/bb842062