Installing Windows Help

I'm fairly certain that's not going to work--to run the Windows installer it essentially needs to have the disk read as if it were on an internal, bootable drive. I'm not so sure that a disc mounted via TDM in another Mac is bootable at all--I don't think it sees the mounted computer's drive as an actual optical drive, rather than just external storage. Regardless, I'm nearly certain it won't work with Windows. I don't even think Windows would install via a "real" firewire optical drive, though I admit I've never tried.

You could confirm by starting up the MBP with the option key held down and see if the external disc shows up in the boot list (a properly working Windows install disc should show up at that point).

As for a better suggestion... no guesses. Is your brother's laptop an Intel Mac? If so, you might be able to install Windows on your MBP with the MBP mounted via TDM, although I'm not too optimistic even that will work.

Incidentally, if I'm wrong and you can get some variant of TDM and Windows installation working, please post with how and what worked, since it'd be useful info to have.