Allocating beyond 4GB using awealloc.

I have awealloc driver 1.5.3.5 that installed with ImDisk. I followed the directions to enable it:

sc config awealloc start= system
net start awealloc

I have 6GB of memory on a Windows Vista x86 SP2 system. Vista can only see about 3.5GB. What I want to do is use everything above 4GB for a ramdisk for readyboost. When I try to create a ramdisk 2GB in size it does not work:

>imdisk -a -f \\.\awealloc -s 2G -m R: -p "/fs:ntfs /q /y"
Creating device...
Error creating virtual disk:
Not enough storage is available to process this command.


The event viewer shows:
Error allocating above 8 GB.
Error allocating above 6 GB.
Error allocating above 5 GB.
Error allocating above 4 GB.
Error allocating physical memory.

The biggest drive I can create seems to be around 1300MB. And that may or may not work, depending on just when I execute the command. So is Windows already using that extra 2GB of memory?

Thanks