DOUG, OK, now I've got some information to work with. I'll provide some information on each topic, with somewhat more precise terminology and detail:
PLUG ADAPTERS: As it appears that you're travelling from the U.S., you WILL need Plug Adapters in order to "adapt" the North American style plug to those used in Europe. Keep in mind you will need
different Adapters for the U.K. and "mainland" Europe. You will also need to determine (by checking your appliances) whether you need "grounding" or "non-grounding" Adapters (one will have two pins, the other will have three pins). The Plug Adapters are simply a mechanical means of adapting the different plugs / receptacles used in the different areas, and have nothing to do with volts / amps / watts. You may already have all this information, but I wanted to give you a precise idea what you will need. If you haven't bought Plug Adapters yet, check Radio Shack stores, Travel stores or
www.magellans.com.
VOLTAGE CONVERTERS: You
may or may not need Voltage Converters. This will depend entirely on the design characteristics of the devices you will be taking with you. You will need to check the "nameplate data" of
each device you plan to use in Europe (look for something that refers to the input voltage). If it indicates 115 VAC (or something to that effect), then you will need a voltage converter / step down device. If the nameplate indicates 100-240 VAC (or something to that effect), then the device is designed to work on both electrical systems and should only need a plug adapter. Do NOT ever plug a device designed only for 115 VAC into a 240 Volt electrical system -- a flash, a loud "snap" and a puff of smoke will signal the permanent demise of your appliance!!!
There is also a frequency difference in the electrical systems (60 Hz in North America, 50 Hz in many other parts of the world) but in most cases this is not a problem unless the devices uses the frequency for reference (such as a clock).
One very important point to make regarding voltage converters, is that two main methods are used to "step down" the voltage from 240 to 115 VAC. One method uses a Transformer, which is a very simple concept. However Transformers are inherently heavy, so the larger ones are not ideally suited to travel. This method of conversion is best suited for electronic devices, where an accurate sine wave is needed.
The second method uses solid-state methods to "step down" the voltage. These are much lighter and more compact, however they produce a very "choppy" sine wave so are best used with "brute force and ignorance" type devices such as heating appliances which are a simple resistive element. Best not to use electronic devices with this type of converter.
There are Voltage Converters on the market designed for travel which contain
both conversion methods. These are fairly compact and light, as they use only a very small Transformer. Some of these are designed to automatically select the type of conversion, others require the user to operate a switch. Check Magellans for an example of this type of unit. One final point to make on Voltage Converters -- many of them are designed only for "intermittent" rather than "continuous" operation. It's probably not a good idea to leave them connected for long periods of time, and I always feel it's a good idea to monitor these while they're connected to the mains / electrical system.
Again, whether you even need a voltage converter will depend entirely on what devices you will be taking with you. Many newer Cell Phone and Digital Camera chargers are designed for "universal" use, so only require a Plug Adapter.
BATTERIES: As indicated in the previous Post, batteries seem to be fairly universal. As far as I know, an "AA" battery bought in the U.S. is the same as one in England or Europe. The voltage should be the same. The amperage is not as much of a concern, as the device will draw as much current (amps) as it was designed for. The only thing you might be concerned about is the amp-hour rating of the batteries (this is not applicable to alkalines, as they're pretty much all the same).
Which brings me to my next point. If you're travelling it might be more cost effect to pack some NiMH rechargeable batteries for your MP3 player, rather than plugging alkalines into it for the whole trip (you could always pack one set of alkalines for "emergency" use?). The design voltage of most rechargeables is a bit lower than alkalines, but most devices funtion quite well with these. It's desirable to buy NiMH rechargeables with an amp-hour capacity higher than 2200 mAh, as this will provide more operating time than the lower capacities. Magellans and Radio Shack both offer "travel" Chargers that operate on both electrical systems and charge batteries in one-two hours, as well as high capacity batteries (2200-2500 mAh).
One other point to mention is that I've heard that NiMH batteries have a high "shelf discharge" rate, which means they will lose some power every day just sitting on the shelf, not being used. This is just a characteristic of this design, and doesn't indicate a flaw. It's a good idea to "exercise" these a few times when you first get them, and then pop them in the Charger on a regular basis to make sure they're at full charge before you use them. For the most part, they don't exhibit the same memory effect as the older NiCad batteries.
Sorry about the very long reply, however I wanted to provide as much information as I could on travelling with electrical devices. Hope this has answered your questions. Happy travels!!!