If you have not yet installed, then don't worry about it. The installer lets you choose LVM as an option. Then you can add your harddrive as a physical volume and then make it the logical volume. From there you can create volume groups, which are analogous to partitions but can be resized at will. The installer walks you through the whole process very nicely. -Roberto
I have to disagree with the last statement (The installer walks you through the whole process very nicely). I've recently installed 2 Debian machines using the new installer. Both times I thought about using LVM because of it's advantages so I selected that option to have a look at it. It just confused the hell out of me to the point where I gave up and did a numpty single partition ext3 install (/ and swap separate). It's a shame because I would have really liked to have tired LVM. I would say that is the one weak point in an otherwise great installer.
Graham