How to enable more than 4 GB in Windows 32 bits

How to Enable PAE Phisical Address Extended RAM  Memory

But hey, it can be useful where 64 bit is not possible because of a 32 bit processor, so why not. Here goes, this option is compatible with any Intel Pentium Pro, Pentium II, III, 4, Core, Core 2, Core i7 and + processor, along with every recent AMD processors and Athlon series.

Windows XP

1. Open an explorer window
2. Tools > Folder Options > View Tab
3. Check the radio box written “Show hidden files and folders”
4. Click OK to accept changes and close the dialog box
5. Go to your local drive where Windows is installed, most likely C:
6. Locate the file called BOOT.INI
7. Right-click on the file and click Properties
8. In the Properties dialog box, make sure the Read-only attribute is unchecked (checking it will prevent you from modifying the file)
9. Click OK to accept changes and close the dialog box
10. Open the BOOT.INI (default opens with Notepad)
11. It should look something like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINNT=”Microsoft Windows XP Professional” /noexecute=optin /fastdetect

12. Append at the end of last line the following: /PAE
13. It should now look like this:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINNT [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINNT=”Microsoft Windows XP Professional” /noexecute=optin /fastdetect /PAE

14. If it does, save the file, exit Notepad and restart Windows
Congratulations, your Windows XP system now runs with PAE enabled.

Windows Vista / Windows 7

1. Click on the Start Orb
2. Search for CMD
3. Right-click CMD or Command Promt in the search results and click Run as administrator4. In the command line, enter:
bcdedit /set pae ForceEnable
5. Close the command line
Congratulations, your Windows Vista/7 32 bit system now runs with PAE enabled.
To install PAE on a specific boot if you’re using a dual/multi-boot system, refer to the MSDN BCDEdit /set command documentation for instructions on how to set the ID of the boot.
Note: Official Microsoft documentation does not as of this writing specify explicit support for PAE in Windows 7.

Source: http://pacoup.com/2009/05/27/pae-vs-64-bit-what-manufacturers-dont-want-you-to-know/comment-page-1/