Winxp sp2 c partition unknown

this normally happens when the c partition is not formatted or there is no primary partition, so when you insert the cdrom you should get the option to format the drive or set up the primary partition.

The only other problem can be if you are using an SATA drive and you have not pressed the relevent F6 key on the start of the installation for SCSI drive support at which point you will be asked for drivers.