It is indeed possible to remove the 512 MB installation requirement, however I wouldn't recommend installing Windows Vista/7/8 without at least 1 GB. Note I'm not sure if this works in Windows 8, but since the installers are similar it should.
Download a hex editor and extract the Windows setup ISO. From there, open said hex editor and load up the file "winsetup.dll". I believe it's found in the sources folder. Find the string (should either be able to use a search function or press Ctrl+F) "77 07 3D 78 01". Simply replace it with this "E9 04 00 00 00". Save the file and repackage the ISO.
Alternatively you could load the ISO into vLite and enable installation of 256 mb of ram. If you choose to do this, make sure not to change anything else as vLite was only made to work with Windows Vista - things will go wrong.