Read the post to the end, before you start to change your disk.
Print anything you could need.
The first thing is to stop apache/httpd, because it uses /var/www.
Make this change permanently, by using chkconfig to turn off httpd/apache.
After that you can umount /var/www. "umount /var/www"
Uncomment any references to hda2 in your /etc/fstab to avoid the system mount it again in the next reboot.
Now, using fdisk, change the /dev/hda2 partition type from Linux (83) to Linux LVM (8e).
Reboot the computer, so the kernel can see the new partition table.
Make sure apache is not running and /dev/hda2 is unmounted.
The Linux Documentation project has a good Howto for LVM: read it !
Create a physical volume on /dev/hda2: "pvcreate /dev/hda2".
Now, add the /dev/hda2 to the existing VolGroup00: "vgextend VolGroup00 /dev/hda2"
now, write down how big is the VolGroup00 in PE: "vgdisplay VolGroup00". Look for a string "Total PE". Note that "Free PE" is a non-zero number.
Allocate that space to the logical volume: "
lvextend -l<put the total PE here> /dev/VolGroup00/LogVol00"
Now you need to extend the filesystem on /dev/mapper/VolGroup00-LogVol00.
The proper command depends of the filesystem.
For ext2/ext3 systems: "resize2fs /dev/mapper/VolGroup00-LogVol00"
For reiser: "resize_reiserfs /dev/mapper/VolGroup00-LogVol00"
For that the file system must be offline. To do that you will beed a liveCD.
After that, create /var/www again, restore the backup and create /home.
good luck and post any questions before you start.