There is no way to natively run Windows 7 unmodified on a cell processor like the PS3 has.
The only way to run Windows 7 natively would be to update the Windows 7 code to run on a cell processor like the Linux kernel code has been updated.
The trick is that no body outside of Microsoft has the knowledge and source code to do that.
The developers that added support to Linux had the knowledge to add cell processor support to it and did so.
The only developers that could add support to Windows 7 would be the ones on the "Windows 7 development team" because of reasons listed above.
It is quite possible that someone could have run a visualization software within a Linux system on the PS3 and booted Windows 7 inside of it but that could hardly be called running it on a PS3 as Windows 7 would be using virtual hardware and have no way to use the cell processor.