And another question:
On my hdd I have:
First partition- NTFS partition (primary) Ė for windows XP
Second partition- boot partition (for grub)
Third partition- ext3 partition for RedHat 9
Fourth partition- swap partition for RedHat 9
If I want to install slackware I will resize the NTFS partition but how can I install slackware without affecting the grub configuration or others partitions?
Don't forget about the primary/logical partitions. If you have all primary ones, you have a problem, because only four are allowed (you can put way more logical partitions, see the partition howto @ www.tldp.org
Note that adding a new partition between others will change their numbers. The ones after it will go up. Example: You had hda1-win,hda2-RH,hda3-swap. Squeezing another in will make you end up with hda1-win,hda2-slack,hda3-RH,hda4-swap. As you can see, RH is no longer hda2, it's hda3. You will have to edit Red Hat's configuration to reflect this, ie edit the /etc/fstab file and /etc/grub.conf file. Choose not to install lilo with Slackware, then you can add an entry for it in grub.