I found out how to create a Swap Logical Volume: 
http://elibrary.fultus.com/technical/index.jsp?topic=/com.fultus.redhat.elinux4/manuals/rhel-sag-en-4/s1-swap-adding.html


11.2.2. Creating an LVM2 Logical Volume for Swap

To add a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want 
to add):

    1.

       Create the LVM2 logical volume of size 256 MB:

       # lvm lvcreate VolGroup00 -n LogVol02 -L 256M

    2.

       Format the new swap space:

       # mkswap /dev/VolGroup00/LogVol02

    3.

       Add the following entry to the /etc/fstab file:

       /dev/VolGroup00/LogVol02   swap     swap    defaults     0 0

    4.

       Enable the extended logical volume:

       # swapon -va

    5.

       Test that the logical volume has been extended properly:

       # cat /proc/swaps
       # free






Ioannis Vranos wrote:
> Based on the following information from Alex Finch I managed to reduce 
> the size of the LogVol00 to 70GB, leaving a free space total of 4.41 GB 
> on the dev/hdc hard disk.
> Since the swap file occupied space on /dev/hdf, I removed it via 
> lvremove /dev/VolGroup00/LogVol01.
> 
> 
> There is a new question now. How can I create and activate a swap file 
> on VolGroup00?
> 
> 
> 
> Alex Finch wrote:
>>
>>  If you look in the LVM howto, you find this>>
>>
>>  11.10. Reducing a logical volume
>>
>> Logical volumes can be reduced in size as well as increased. However, 
>> it is very important to remember to reduce the size of the file system 
>> or whatever is residing in the volume before shrinking the volume 
>> itself, otherwise you risk losing data.
>>
>>
>>
>>       If you prefer to do this manually you must know the new size of 
>> the volume in blocks and use the following commands:
>>
>>       # umount /home
>>       # resize2fs /dev/myvg/homevol 524288
>>       # lvreduce -L-1G /dev/myvg/homevol
>>       # mount /home
>>
>>
>> In order to do this you need to boot from a live cd,
>>
>> I guess you need
>>  resize2fs /dev/mapper/VolGroup00-LogVol00 80G
>> and
>>  lvreduce -L80G /dev/mapper/VolGroup00-LogVol00
>>
>> not sure what your /dev/VolGroup00/LogVol01 is for though. You may be 
>> able to remove it (lvremove /dev/VolGroup00/LogVol01)
>>
>> if you get it right when you do vgdisplay -v it will show  /dev/hdf1 
>> has Free PE = Total PE = 894, so you know it is safe to remove it.
>