OK, here you are:
1. when you still had Vista, your C partition was the Vista OS and your D partition was the Vista recovery partition. That is how the OEMs set it up.
2. now you seem to have installed your Windows 7 on D - but your Windows 7 MBR is probably on C - so you ended up with a mix-up
3. when you install Windows 7 from and OEM disk, you should end up with one partition provided you start with a clean disk
4. Here is what I suggest:
a) make an image of your Vista partition for the case you ever want your Vista back. Use
this program. If you think you never want your Vista back, you can skip that.
b) Cleanup your whole disk (delete all 3 partitions) and reformat (quick format) the disk with
this program. Define the whole disk as one partition (that way you avoid the 100MB boot partition at installation time). Burn the bootable CD (see left pane on the webpage). Then it is easy to do.
c) reinstall your Windows 7 in that partition.
Note: I did not recommend to image and reload your current Windows 7 because I suspect some mixup with the MBR.
PS: If you need more help with my other tutorial, send me a PM.