You want to format the c:\ partition or the entire system with all it's partitions?
To format c:\ boot with the Windows install disc, and select a fresh copy to be installed, and when prompted to he path, select c:\, and do a NTFS format.
To format the other partitions, right click in My Computer the partition itself and the select Format.
Hope this helps, haven't actually reinstalled Win for some time now, it's all a bit foggy.