Is there a tutorial anywhere on how to do transparency/alpha planes?
I'm using Carrara 5 Pro.

Alpha maps are basically developed on the basis that black is transparent and white is solid visibilty and any grey tone variation between the two represent the depth of transparency.

Hope this helps..

 OK, but how do I load a transparency map?  In Carrara, in the shader thing, the transparency option has no place to load a map. If I select "texture map" it uses the texture map as a transparency. I can't figure out how to have separate texture and transparency maps.

In the shader room, set the Transparency channel to MAP and then load it the same way you would a texture map.  You can also do things like mix it with a color channel or multiply it with a color channel to make only certain colors transparent using the map.  It's too bad that Daz hasn't gotten around to releasing a real user manual for Carrara.  It would help out a LOT of new users.  Most of us learned on our own, the hard way.  Don't give up.  You will figure it out eventually.

Quote -  OK, but how do I load a transparency map?  In Carrara, in the shader thing, the transparency option has no place to load a map. If I select "texture map" it uses the texture map as a transparency. I can't figure out how to have separate texture and transparency maps.

 When I select "texture map" in the transparency channel (there is no option for just "map") it uses the regular texture (I can have either a texture map or a transparency map, but not both). 

If you create a jpg (within and external program) representing the transparent within your object and then upload it into the Alpha channel using the "Map" option it will then complete the transparency required. However... it is advisable to learn about UVmapping other wise you may not get the effect you wish for. You have to realise also that a tranparency map and texture map are exactly the same, just a jpg or similar image format that offers the transparency range using a variation of tones between black and white.

In Carrara any bitmap image is considered a "texture map". If you're working with Poser hair for example, the diffuse image should be plugged into the Color channel and whatever transmap the merchant made should be plugged into the Alpha Channel.
If you're making your own stuff, just make sure that your diffuse/bump/spec/transparency maps all have unique names.
Hope this helps!

 OK, I got it  now. Thanks for the help

You're welcome

 I've also prepared a tutorial that you can see here.
Mark