You are more or less correct...partitioning is actually done by the OS. I think what you mean is won't delete the RAID array. The OS will still need to create a new partition or to repair the installation if it is still somewhat functional on the old boot partition.
Yes, upgrade to Win7. It is much more stable than Vista and its compatibility with software and drivers is much better.
If it were me, I would still remake the partition in the BIOS. It just makes things cleaner. Hard drives and BIOS do a lot funny-business under the hood where you can't see it...mostly having to do with the boot parameters and such. A clean creation of the RAID would make sure everything is done from scratch. This approach may seem almost superstitious, but this is a windows computer. ;-)