1. Backup your windows using any tool that is capable of doing so (Acronis TrueImage, partimage on sysrescuecd, plain block copy with dd, etc.)
When using file backup you should also backup the MBR of the disk with a linux command like dd if=/dev/sda of=mymbr count=1 bs=512, as it helps to restore the boot record if anything goes wrong.
2. Resize your windows partition (There are different ways, either do it by software like Acronis DiskDirector or delete the partition table, create a new smaller partition and restore your windows backup - that only works, when it's a file based backup, doesn't work with dd)
3. Boot tc on your pc, create a new partition after the windows partition, type 0x83, format with ext3, follow the steps in the installation procedure
4. Install and modify grub boot loader, Windows can be added to menu.lst using the principle of "chainloading" and it looks like this:
title Windows 7 Professional
rootnoverify (hd0,2)
chainloader +1
makeactive
5. Now grub should always start, leaving you the option to start either tc or Windows.
__IMPORTANT__ Do NOT modify your system, when you're not 100% sure to have a backup, which can reverse any failure.