From what I've read and seen it is possible to have 2 or more on the same partition, although it's highly not recommended.
Using the XP disc you will be able to see the partition and delete it, followed up by formatting. You can then start fresh.
I run both 2000 and XP Pro on the same machine, but on different partitions.
Follow the link below and read carefully, there is all you need to know found within.
Black Viper