Description of problem:
    It seems that qemu-kvm supports only 2G memory for guest on 32-bit systems, if I give it more than 2047MB, virt-manager doesn't report an error immediately, but a traceback after create the guest or when starting it.

Version-Release number of selected component (if applicable):
    * kernel-2.6.33.1-19.fc13
    * libvirt-0.7.7-1.fc13
    * python-virtinst-0.500.2-3.fc13
    * qemu-0.12.3-6.fc13
    * seabios-0.5.1-1.fc13
    * virt-manager-0.8.3-2.fc13 

How reproducible:
    Always.

Steps to Reproduce:
1. Setup a i686 host system.
2. Create a Virtual Machine with more than 2047M memory(eg. 2048M).
3. Go next and start the machine.
  
Actual results:
    A traceback with message:

    Unable to complete install '<class 'libvirt.libvirtError'> internal error Process exited while reading console log output: qemu: at most 2047 MB RAM can be simulated

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/create.py", line 1510, in do_install
    dom = guest.start_install(False, meter = meter)
  File "/usr/lib/python2.6/site-packages/virtinst/Guest.py", line 798, in start_install
    return self._do_install(consolecb, meter, removeOld, wait)
  File "/usr/lib/python2.6/site-packages/virtinst/Guest.py", line 899, in _do_install
    self.domain = self.conn.createLinux(install_xml, 0)
  File "/usr/lib/python2.6/site-packages/libvirt.py", line 1147, in createLinux
    if ret is None:raise libvirtError('virDomainCreateLinux() failed', conn=self)
libvirtError: internal error Process exited while reading console log output: qemu: at most 2047 MB RAM can be simulated

Expected results:
    Friendly message when memory >= 2048, or upper limit for the memory-input textbox.

Additional info:
    None.