2010-10-14, 07:28 AM
Welcome back! :)
I'm not too familiar with using NTLDR to boot GRUB; I know much more about doing it the other way around. It is reasonably easy to reinstall GRUB these days if a Windows install wipes it out, provided you just keep a live distro handy. I don't do it all the time, but I have on several occasions reinstalled Windows in a multi-boot setup environment, then booted a live CD to reinstate GRUB afterwards.
If you do go down the NTLDR->GRUB route, (again, not something I've done or am familiar with!), I do know you can install GRUB to a specified location from within the Ubuntu installer. I haven't checked it with the latest version, but it always has been there at one of the last few screens of the installer.
As for the sizes of your partitions, I'd imagine 500 MB to 1 GB should be plenty for /boot, swap is usually recommended to be about 1.5x as large as your RAM, so 6 GB?
To try and answer some of your other questions too -- you can have a single swap partition. In my experience, multiple distros can 'share' the same swap space (obviously not at the same time, but that isn't an issue!).
As far as sharing /boot, GRUB has changed signficantly in the last few years -- there is now a new GRUB 2 version that some distros are using, which is quite different to the old GRUB (see this blog post I made). That might affect your plans, but again, sharing /boot between different systems isn't something I'm too familiar with either. I do have a super-duper ridiculous multi-boot setup, but each OS lives in its own partition, and I have one OS which acts as the GRUB 'master' -- its configuration file contains the GRUB commands to boot the kernels for other OSs (those kernels and initrds being stored on the relevant partition for that OS).