Sculpties...?

Ok, I know what a sculpted prim is, and how to create one, but I do have a few key questions that are really baffling me.... (a few blender questions too)

1. How do you keep straight lines in a sculpt actually straight?

2. how do you export a texture from blender that you paint on your sculpt?

3. How do you keep multitires on level 2 and under yet STILL keep detail?

4. How do you link meshes into one another so you can smooth them down together in one piece?

Any help is really appreciated ^^

You...just don't curve it. For instance, if you want 4 edges in a straight line on the X axis, you could scale to 0 on Y and Z. They'd then be a straight line. If you mean how do you keep them visually sharp, bring another edge very close to it. SL uses smooth shading for sculpts, and doing this makes the shading for the corner tiny, giving it a sharp look.

(Assuming Texture Paint, not Vertex Paint)In the UV/Image Edtor (It should be showing your painted texture), just Image > Save As.

If using Vertex Paint instead, then first make sure the Material allows Vertex Paint to affect it. In the Materials panel, just make sure that 'VCol Paint' is depressed. Then, open a new image of your preferred size in the UV/Image Editor (While you have it all selected in Edit Mode). Finally, go to the Bake tab of the Scene panel, and click 'Bake'. You may want to select Textures, or Full Render, depending on if you have lighting set up, etc.

Multires saves the higher levels of detail. If you go to 3, and make small changes, then back down to 2 and back up, those small changes will still be there. I'm not sure what you're asking.

You don't. At least not for sculpts... you can't combine meshes and still expect it to bake into a sculpt map properly, if at all. BUT... in general, to do it, first make sure they're the same object. In Object Mode of Blender, select both and press CTRL+J to join them.

Next, arrange them how you want. Try to align as many vertices as possible, and have open ends touching. Then, Remove Doubles (W > Remove Doubles). This will combine the meshes at any vertices that are on top of each other, or very close to each other. To increase the allowed radius, go to the Tools tab of the Buttons Window while in Edit Mode. Where it says 'Limit', increase the value to whatever you want.

If you didn't have open ends, then there will be inner faces that will mess with things like Catmull-clark Subsurfing or Multiresing.

In addition to what Keira says:

ALso take care that straight lines will keep straight only when they go along one axis. You can make an experiment: create a cylinder, do not close it at the ends.
bake it as it was created and look at it in SL. it is ok, the ends are straight.
Now rotate the cylinder by 31 degrees along the y axis, bake again and look at it in SL. The ends have become rough...

instead of removing duplicates at the end, you also could ripp the meshes apart again. So you get a couple of perfectly aligned objects, which you can bake and rearrange as multi sculptie creation. But beware: There is a problem with alignement. You can't expect to keep the perfect alignement with your final sculpts. That is because they have limits in where exactly the individual vertices can be placed (due to the 256 bit color range per axis.)