There are two ways you can approach this:
1) Keep your existing Linux install, and install Windows as well (this is harder)
2) Wipe your hard disk and install Windows first, then Linux (this is easier and slightly safer, but you will need to back up your files first).
I'll describe option 2.
First, back up your files to CD or to another computer or disk.
Delete all the partitions on your hard disk, then save the partition table. At this point, your system is completely unusable, and you'll have to reboot with the power button.
Insert the Windows CD and install Windows.
Download or buy a more recent distro of Linux, then install it. I'd recommend either the SuSE download version (http://www.suse.com/us/private/downl...ux/index.html;
follow the instructions on the page for the download version, not the personal version) or Mandrake (www.linux-mandrake.com;
download the ISO, burn it to a CD and install). You can also get distros from magazines or various other places if you don't have a CD burner.
I don't recommend sticking with SuSE 8.1 (because of performance, security, less good hardware support, less usability and so on) but if you do then be prepared to have to repartition your hard disk with the SuSE installer before installing Windows, then installing SuSE after that.
In any case, don't try and install Windows last because Windows overwrites the master boot record, making Linux unbootable.