It doesn't really matter what version you actually use, but you will need to read around some of the newer / older features. I normally run fairly recent versions of Linux distributions, but then when I've been revising I've read up on some of the older things.
The majority of the information won't have changed, it's just a few things that you need to know. I found following some threads on the forums (on this site), or searching the web is useful. A particularly good place is The Linux Documentation Project
, as many of the Howtos cover some of the older / more generic methods that the exam asks about.
One example LPI has only just included cups (printing) in the latest version of the exam, but cups has been used by most distributions for some time. You can learn most of the cups stuff playing with your linux machine, but should still read up on some of the lp / lpr commands for the exam (for the 102 exam).
Another example is that most distros have now moved over to the GRUB boot manager, but questions still ask about LILO which was the most common a few years ago. So play around editing your GRUB config on your machine (although be careful!), but read up about the LILO config file, and the important bit is knowing that you need to refresh lilo whenever you make a change by running /usr/sbin/lilo (not required for GRUB).
These differences are only a fairly small part of the exam (except maybe the lilo bit). Actually getting hands on experience using Linux is the best way to learn linux, then just read around, based on the list of important subjects/commands/config files to prepare for the exam.