How to use Logical Volume Management

I've just installed SuSE 10.0 beta, using LVM for most of the partitions. I was of the understanding that LVM allowed for the resizing of partitions, without shutting down the computer etc. However, when I try using LVM in Yast, I get an error message, that changing the partition size may result in loss of data. When I tell it to proceed, no change is made. I get similar results in Partitioner. There is some free space in the volume. What am I doing wrong? Have I misunderstood LVM? tnx jk