Uninstall Vista from xp/vista dual boot and install windows7?

I have xp/vista dual boot. I want to remove Vista and install windows 7. So that I have xp/Win7 dual boot. I have xp and vista in separate partition as of now. I want to have the windows 7 in the same partition where Vista exists.
How can I do this. Please let me know.
Update: Juli,
I dont know how will it behave with the boot loader. I dont want to take any risk as I am very scared of these MS softwares :(.

It would be great if somebody lets me know a step by step process.
Thanks in advance for your help.
4 answers 4