Howdi,
I am not sure if this will be helpful to you but give it a shot!
When I first installed my RH 7.2, I had Win2k first installed and running on the machine, running throug the RH installation process, first I used the automatic partition for Linux (this was Linux took whatever it need for partitions and mounting automatically without screwing Win) then I chose to use LILO which is the boot manager so when you boot up first time or whatever time, LILO comes up and asks you to choose what to boot of! so easy and simple, this way you'd have dual boot with Win and Linux.
Now the Gnome issue thing, I am not sure but activating boot sectors and so may could have screwed some of the system files or so. as I said I am not an X-pert yet! I always used KDE since it is a lot more popular and has a lot more utility to it.
Well that's about it. Give it a shot if you want and let me know.
Regards,