|How do I Format Drive C: ?|
You boot from a CD/DVD and do it from there. Normally Windows resides on drive C: and it will not let you format it while Windows is running. Suicide is not permitted.
Does it have to do with DOS ?
It has nothing at all to do with DOS, DOS is an Operating system in its own right ans we are talking about Windows XP. The text based b/w window you get when you run Cmd is not DOS. Its is a command prompt which just by chance happens to have a similar command prompt to DOS.
how can i remove a partition that i made by mistake???
Go to Disk Management and delete it from there.