Ah, the elusive Grub splash screen - took me a wee while to figure that one out after a different distro over-wrote the pretty carbon-look Mint one. Have a look at the files in /usr/share/doc/grub-gfxboot. [Note: just to be a real pain, the splash image wasn't included in Mint 6 - only on the CD].
Startupmanager (found in Synaptic) might be what's loaded by default in Ubuntu (check if installed). If so, then you could install it in Mint and see how it goes.
🙂
Re-partitioning is always going to be an issue, due to the myriad of configurations that are possible. Most likely this is down to the installer assuming the OS is to be installed into the first HDD (a normally fair assumption).
Advisable to always "keep your wits about you" during the partitioning process and not press buttons "willy-nilly"
😉 The latest installation routines are pretty good at guidance and a far cry from having to work out cyclinder boundaries etc. manually, as in the past.
I have to admit that I generally use a Windoze utility to re-partition - not that gparted isn't capable - more to do with flaky Windoze' handling of partitions.
Truff: try booting from USB? (See opening post).

Just skimming the surface
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Demised responsibility