Most Linux LiveCDs have a partition editor on them that you can use to partition your hard-drive. I was able to partition my drive into three sections: a Windows-bootable section (NTFS), a Linux root section, and a third for shared data between the two (both using EXT3 - there is a download for Windows that allows it to recognize this filesystem).
Usually what you need to do is resize your Windows partition first, as on most configurations it takes up the entire drive. Typically, this will not cause any loss in data, though you may need to defragment your drive first. I personally had to run chkdsk and reboot Windows twice for the partitioner to allow me to resize. Also, it is a good idea for you to back-up whatever data you have on it before proceeding. While resizing the NTFS partition is fairly stable, there is a slight chance that it may mess up somehow and make that partition unbootable. Be sure to exercise good judgment, and remember that there are IRC/IM programs included on most LiveCDs, so you can always ask for assistance during the operation.