I bought one for a previous trip that says So Europe (etc)...can I use it in Czaech R, Hungary, Croatia, Slovenia and Austria as well or do I need an additional one?
I assume the "So Europe" you have means southern Europe? If it's the two rounded prongs, you should be OK.
Here is a link for the World Electric Guide:
I purchased an iPod and digital camera for my trip this summer. They both say 120 to 240 on the plug/charger. Does that mean that I just need a European plug adapter for them, and not a converter to adjust the voltage?
Yes, for items that say both voltages, you only need the plug adaptor.
I used the two-round-prong adapter to charge Canon digital camera batteries in Italy, Austria, Czech Republic and France with no problem. The voltage converter is in the charger itself. Check you camera and IPod owner's manuals.
I also had a charger for AA batteries for a Walkman-type radio and cassette player. That did NOT work, presumably because that charger was designed for US domestic use and didn't have an internal voltage convertor. Unfortunate, because batteries are very expensive in Europe.
http://users.pandora.be/worldstandards/electricity.htm has better descriptions of the different styles of plugs.
Based on measurements I made at the local hardware store, the So European plug has 4.0mm (5/32) diameter pins. The countries you mentioned use French or German spec plugs with 4.8mm diameter pins, but they will also accept 4.0mm diameter plugs. What I use is called a Europlug, which is supposed to work all over Europe. As far as I can tell, it is identical to the So European plug.
If you frequently travel to the same destinations, consider purchasing travel appliances from that country. That way there is no concern over voltages or plugs.