Yes, you normally need to delete individual partitions before you can resize and reformat them, and Win2K and WinXP have easy facilities for doing that on their installation CDs (forget about FDisk, as that's history now, and was a pig to use, anyway). So, run the XP installation CD and, at the appropriate point in the Setup (it'll become obvious) delete the existing partitions. You'll of course lose all your existing data, so ensure you've made a backup of important data beforehand. Within the same procedure, repartition the hard drive and also reformat the partitions.
BTW, I think you meant "un-partition", didn't you? Not "unpartician".