Total memory you can use in 32-bit Windows= 4GB
You have AMD card = 1GB. Remains = 3 GB
Your computer is showing 2.75 usable, so 256 MB is being used by some other device.
256 MB some device + 1 GB GPU + 2.75 usable = 4 GB
The un-official patch you mentioned basically makes Windows ignore the 32-bit limit. But it has no effect because the 32-bit instructions for Windows and CPU cannot handle more than 4GB memory in total.. The applications in 32-bit OS cannot use more than 4GB in any case.
This page explains technical limitations even after you patch the kernel : http://www.geoffchappell.com/notes/windows/license/memory.htm
Only way you can make use of more RAM is to upgrade to 64-bit Windows.