Well, if you overwrote your XP partition, your data is gone. Next time be sure to back up your data first!
Sorry about that...
On to dual booting, your new mission, should you choose to accept it is to find your XP disks. Here is what you want to do:
1) use knoppix Live CD and qtparted (a nice graphical partitioning program) to create the following partitions:
/dev/hda1 NTFS for windows XP ~10GB
/dev/hda2 ext3 for /boot ~100MB
/dev/hda3 swap 2x your RAM (but don't go over 1GB, you won't need it)
/dev/hda4 ext3 for /home ~5GB
/dev/hda5 ext3 for main linux partition ~10GB
/dev/hda6 fat32 for sharing files between linux and windows (I'd use the rest of the disk depending on what you plan to share -- mp3's, etc)
2) Install XP to the NTFS partition
3) boot into XP and get it working the way you want
4) Install Debian, at boot:
to get a newer 2.6.8 kernel, DO NOT overwrite the NTFS partition, do manual partition and point /home to /dev/hda4, /boot to /dev/hda2, swap to /dev/hda3 and / to /dev/hda5
5) install Grub to the master boot record
I'll see if I can find a link to help you with the installation walk through...