Here is a pastebin link to the boot-repair diagnostic. I have not run boot-repair because it looks like it might be set to overwrite all drives by default and I don't want to lose the ability to avoid using Grub.
I have tried to dual-boot Ubuntu a few times in the past and it's never worked out. Today I have spent many hours installing and reinstalling for various reasons (including initially installing the 32-bit version, then having a working 64-bit install, then upgrading to 12.04 to have it all bork again).
The current state of play is as follows...
sda has two partitions, I can boot into Windows 7 if I choose this drive on startup. To fix this I tried to install lilo on the drive. I thought that didn't work and that I fixed it with Windows tools but the boot-repair diagnostic says that it's running lilo. I'm just happy it's working at all!
sda1: the Windows 7 system partition
sda2: the Windows partition itself
sdb has four partitions, booting this gives me Grub which has a working entry for Ubuntu 11.10 and a non-functioning entry for W7
sdb1: has music etc. on it that I access from Windows
sdb2: is a FAT32 partition that I thought I might need to transfer files between OS's
sdb3: turned up somewhere in installing Ubuntu, not sure what it's doing
sdb4: this has Ubuntu 11.10 on it
sdb5: is a swap partition
Ideally, I would like to be able to boot from sdb by default when I start my computer and be able to choose between Ubuntu or Windows 7 there, whereas at the moment the Windows 7 entry does not work. I've just realised that ideally I ought to have the error message that Grub gives here, but I need to reboot to find it, I will edit this post with it in a moment.
Edit: Selecting Windows 7 in Grub gives me a black screen with...
"Error: no such device EXXXXXXXXXXXXXXX" (this advances faster than I could note those letters/numbers, but it started with an E)
"BOOTMGR is missing
Press ctrl-alt-del to restart"
I'm now wondering whether the title is misleading, I'm not sure whether MBR and BOOTMGR are the same thing.