I know how to add linux if windows is pre installed. But do not know how to do it in reverse

You'll need to have a rescue disk and a live cd with g/qtparted on it.
Use knoppix to mount the volume externally. Version 5.X not adrianne is to be used.
Let knoppix boot with .
Open a terminal and type in sudo su
then type in qtparted.
Resize the partition to allow enough room for the windows install.
Commit the action.
Reboot after the task is done.
The rescue CD will allow you to reinstall grub.
Install the Windows OS7 on the spare area being sure not to overwrite the Linux partition.
After installing, reboot with the linux cd in the drive.
Replace grub the update through the repository software

The RESIZE option is not highlighted so I can just click on it. I have /dev/sda1 highlighted but it will not allow me to resize. should I create a partition table? it states "all data will be lost".

I started gparted and it gives me the option to resize my boot partition of 200mb /dev/sda1 boot, but will not let me resize /dev/sda2 148.85 gig. When I click on the info button it tells me:

unable to detect file system. possible reasons are:
-file system is damaged
-file system unknown to gparted
-there is no file system available (unformatted)

do I format?

It would be useful to know which distribution of Linux you are using and also what your partitions are. To get the partition info, log in to a terminal as root and run command: fdisk -l (lower case Letter L) and post it here. also, which version of windows, 7, vista, xp??

You need to do an fsck of the file system through the live CD. That way the live CD can recognize the file system and thus resize it.

If it's ext4 or ext3 I believe you can run
After that, resize the partition, install Windows, boot up with the CD in the drive and reinstall GRUB.

Fedora12, windows7

disk /dev/sda: 160.0 gb
255 heads, 63 sectors/track 19457 cylinders
units+ cylinders of 16065 * 512 = 8225280 bytes
disk identifier: 0x00072eb0

device boot>>>>>>>>>start>>>>>>>>>>>>end>>>>>>>>>>blocks>>>>>>>>>>>>>>id>>>>>>>>>>system
/dev/sda1/...........1................26...........204800..............83..........linux
partition 1 does not end on cylinder boundary
/dev/sda2/...........9742..........19457...........70043770...........8e...........linux lvm

You could check this site out. It explains installing vista after Linux already installed so it should be pretty much the same for win7:
http://apcmag.com/how_to_dualboot_vi..._installed.htm

For Vista, I'd recommend defragging your windows filesystem and then resize it in Vista. It will allow you to resize it down to about half the size. I'm sure that you can do the same thing in Windows 7 as well. It is a debugged version of Vista with cosmetic changes in the UI.

On my Gateway netbook which came with Vista on it, I booted to the wrong partition by mistake and reinstalled vista. I discovered that the recovery would install vista into a blank partition. Knowing this, I was able to delete the vista partition, install Linux and then run the recovery. This allowed me to re-install Vista on a partition a lot smaller than I would have been able to resize it down to.

You will need a Live CD, rescue CD or your install disk to be able to boot into Linux (using the grub shell) after installing Windows 7.

If your computer has restore partitions instead of a windows 7 install disc, be sure you leave them alone.

I got it thanks for the help all.