Right now I have Ubuntu 7.10 on my laptop and love it. My friend keeps bugging me to put Windows on it (he's totally anti-linux). I need to know how to repartition the hard drive so that I can dual boot it, XP and Linux. Thanks.

XP requires a primary partition, that's all. I you want to share stuff between them (as in write from both sides) it's safest to set up a partition for that. These days NTFS (using NTFS-3g on Ubuntu) is the way to go.
Your bootloader (in the MBR) will get overlaid - easy enough to fix; hundreds of threads here on LQ.

Actually you need to "resize" one or two partitions in the hard disk to squeeze some unallocated hard disk space. The program gparted inside Ubuntu is the tool.

Once the space is available use gparted to create a primary partition type 7.

Reboot and pop in XP's installer and it will seize it for installing XP. The process will overwrite Ubuntu's Grub in the first sector of you hard disk making it unavailable temporarily. Once XP working successfully you can restore Grub using the Ubuntu Live CD or any live CD. Equally you can amend XP's NTLDR to boot Ubuntu. You will find all the booting instructions in the last link of my signature.

Grub is much easier to work with.