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#21
The Boot flag you're referring to is present because you are booted into that OS at the moment. If you started Vista it would have Boot flag on Vista.
System flag shows us where the boot files are located and they are on the System partition created for that purpose.
Hence you can delete Vista from Disk Mgmt with no problem, recover it's partition space into Win7 using a partition manager like free Partition Wizard bootable CD, or create a New Partition there.
What other partition were you wanting to delete? You cannot delete System partition without first recovering the System boot files into Win7 by marking Active and running Startup Repair up to 3 separate times. System partition likely also contains factory utilities which came with the computer but you may not use, may have only been available in Vista and may have lost their link when you installed Win7.
I would not delete the Recovery partition until you have made the Recovery Disks so you have a way to restore to factory condition if every wanting to sell or gift the computer. If the computer came with Vista, you should be able to make them in Vista under All Programs. It is likely the link to run Factory Recovery from the partition was lost when you installed Win7, but you can try it from boot to see if it cues up to run.