Which JVC did you get? Each model seems to have a different panel layout with different controls. I have the KD-G320... got it packaged with the ipod adapter at Circuit City for a great price, so I figured, why not?
The KD-G320 has a round navigation control to the left of the volume knob. It;s really a four-way clicker... left - up - right - down. With the ipod attached, you must control it via the radio, the ipod itself is locked. Click up to get into Menu. Then click right to go through Playlist, Artists, Albums, Songs, etc. Click down to select. Cick right come more to cycle through choices, down to select. When you get to a song, click down to play. Or, you can set "song random" or "album random" by pressing the mode button (far right on the panel) then preset 6. I usually use song random, and then while playing just click right to skip to next song.
The JVC units only display 8 characters, and mine uses large-segment lcd, which is not very readable, IMO. The Pioneers now have 16 characters. Some of the high end units have dot matrix or OEL displays which would look better I think (but I haven't seen any).
With the aux input on the front of the unit, the head unit is really just a set of speakers, so all you get is the music... no display, and you must control it from the ipod. Some people seem to prefer this.
With the adapter, using the 30 pin plug, you control the ipod from the radio (or the radio's remote if it has one -- mine does, but I never use it). You get the display. What you DON'T get is access to the ipod's other menu items like settings for sound check, eq, etc. I'm not sure if these setting even get passed to the radio at all... I tried setting sound check to prevent wide swings in violume between songs from different albums, but it did not seem to work. I also tried setting the ipod eq to "rock", but I couldn't hear any difference from flat eq.
The MP3/WMA disc player is nice too.... like having a bunc of small ipods. Interface works pretty much the same... click right on the nav button to cycle through folders, down to enter a folder, right (or left) to cycle through the contents, down to select. Sounds pretty much the same as the ipod, which is expected 'cause it's similar encoding. If you name your folders beginning with "01", "02", etc, you can access them directly using the presets. It's supposed to suport 8 levels of of folders, but I haven't tried it yet.
Some people say the sound quality of the ipod isn't great, but it sounds good to me. Definitely better than FM radio, even with a good signal.
What I wish I had is bluetooth through the radio. There are a few of these available... Parrot (better known in Europe), Pioneer and Sony each have one, JVC just announced one this year. Most major players have bluetooth add ons for some of their units (Alpine,Pioneer,Panasonic), but I'd prefer builtin. The Panasonic is incoming calls only
. They are all pretty expensive... but so are the unis\ s with the builtins. Now I use a Motorola visor clip unit, which works OK, but I have to mute the radio myself.
Oh well, guess I droned on long enough.... time to watch "The Office"...