Some very interesting methods here:
http://www.virtualbox.org/manual/ch04.html#additions-windows
Looks much better than overwriting the MSI, which has now failed on me twice.
Start reading here:
http://msdn.microsoft.com/en-us/library/ff556232.aspx
and try /3GB and/or /PAE (search for it in the above) if you’re on XP or 2003. If you’re on Vista or 7, go here:
http://msdn.microsoft.com/en-us/library/ff542202.aspx
and try PAE and very possibly IncreaseUserVA.
I have found very good performance of 32-bit Windows as virtual guest, in a VirtualBox environment hosted on 32-bit Fedora 14 Linux, using the PAE kernel on Linux and /PAE (or BCDEdit /SET PAE) in the virtual. If you use PAE in the kernel, do make sure to use PAE in the virtual, or there will be an extra and expensive memory processing step required at all times. This is to be done even if the virtual is configured with smallish RAM, e.g., 1G.
The following:
http://technet.microsoft.com/en-us/sysinternals/ee656415
creates one or more Microsoft VHDs, suitable for use in Hyper-V and Virtual PC, from the drive(s) and/or RAID volume(s) of a running server or workstation. Server 2003 / XP and up.