How to: 1)Change Drive letter & 2) Put back Boot.ini in msconfig.

Earlier had dual boot C:Vista & D:Windows XP. Now deleted C: Vista using Partition Wizard and reconfigured boot.ini to help boot into D:Windows XP. So far so good but now i am not allowed to change the drive letter D: to C:. I tried Disk Mangement utility and also DISKPART(assign letter) but in vain. How to fix this, any solution. Further to this 'boot.ini' tab is missing in 'msconfig'. So run 'regedit' then checked path HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\MSConfig\state. In right pane deleted all *.ini including boot.ini. Booted the system and again run msconfig all tabs viz. General, System.ini, Win.ini, Services, Startup & Tools appeared but Boot.ini. How to solve this and drive letter problem.