The inside of the speedo and tach on my bike is starting to get all grungy looking.  Is there any way to get that clear plastic off to clean the inside of it?  Any little tricks to it?  Thanks.

This is a way to get into them.  (just disregard the LED stuff)
http://www.gstwin.com/led_gague_lights.htm

So that plastic trim ring will pry off, any other special tricks to get it to come off of there without it breaking?

The black ring is just folded around the plastic on the spedo.  I just pryed it up with a screwdriver, then when I was done I just tapped it back down with a hammer.

Someone else suggested using a dremel tool with a cutter blade., and cutting the back of the ring off (where the screwdriver is in the picture) then just gluing the front back on when your done.

That someone would be me. Srinath also had the idea of squirting a cleaner inside the "clock" (euro-speak), swirling it around to clean it up. Rinse and repeat as necessary.

In my work, accessability is a premium. If I am going into something and it takes prying and hammering to put it right, it is not an option especially if you will have to do it again. That's why I just removed the back edge of the aluminum retention ring. I will use RTV to tack it back on.

Whatever works for you is best if it fits your personality and means.
I made a rotating electric table to spin the clock around while filing the edge off the ring. The table also doubled as a test bed for the signal generator test I did. My "Just picked up my GS500..." thread has more information as does my web page.

I guess the larger question has not been asked.
Why do they get grungy inside?  :dunno:

I believe it is because the things are not sealed hermetically. As the back light warms up the housing, the inside air heats up. When you are done riding and shut it off, it cools down. While cooling down, moist outside enters from the back and condenses inside the item. With sufficient cycles of heating and cooling, the stuff stratifies toward the glass and deposits itself there. Add to that the affects of the sun and other heat sources. If you have an old GS, look at the top of the housing where the lamp is inserted. Mine are all yellowed from the heat.

It is just an idea...