How to remove a dual boot drive partition.

I have a HDD that is partitioned into 2 and each contains a dual boot WIN7 OS (both different ). I have backed up the latest one (that I wish to use) but other than successfully removing the dual boot option at startup I cannot find any way of reusing the older partition as a data partition.
It comes down, it seems, to that unwanted partition being a System partition although no longer the BOOT default.
Even with a external Acronis backup of the desired partition I'm loathe to just wipe the whole HDD and repartiition then recover from the archive. Why? Well.. having once lost everything to a seemingly sound backup I prefer to keep the active one on the HDD if it all possible.. If not I may be able to "test" it on another drive.. paranoid? who, me??
Any ideas? please.
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tw33k said:

Could you use the snipping tool and post a screen shot of your computer management screen for us to look at?

What he is going to say is probably best but, what I did when I had a dual boot partition is that I formatted the drive that wanted for data then reinstall Windows 7

tw33k said:

Could you use the snipping tool and post a screen shot of your computer management screen for us to look at?

Sure.. Hopefully the file is there now..

Thanks

As Barefoot says, you'll need to mark C active then boot into Win7 DVD to run Startup Repair up to 3 separate time with reboots to write the MBR to D.

This will allow you to format C for data.

If you want to recover the space from C into D so that D is in the preferred lower HD address, with a new data partition to it's right, post back and we will give you the steps.

Yes..that worked..!:)
I had to boot into repair 3 times before it actually sorted out the booting requirements. I think users should note that when the setup screen says, after selecting Repair, that it may boot the system a few times that in fact it means YOU may have to make it so this.. It would be possible that the unwary would think the first failed attempt was indicating total failure. Never the less, this latest installation/repair interface beats the heck out of the older "Press F8" to continue, or go to the Command line to do Dos type repairs etc, for the uniniatiated.
It seems to me that on a dual boot sytem, partucularly 2 partitions on the one HDD, that the second installed OS is somehow dependant on the first.. I guess this is where the "system" flag comes in?
Anyway, all's well and I've learned alot.
Thanks

Oh, thank you all!
It's good to know the "why" as well as the "how"..
The other thing I've noticed about the Start Repair process.. If it has to, Windows will revert to a system restore point to achieve a solution but you wont be told this until it becomes apparent.. Not that it matters at all as it would have to be manually selected (which is another nice feature "up front" ) but it would be thoughtful if it advised the user just what was going on. Oh, I know..there is a log but I'm talking about the percentage of users that are not savvy enough to seek out the answers.\, or to come here and seek assistance. Still, not complaining, they seems to have got it right..at last .