bvv,

1 - Texture sources
No, there aren't any texture packs available for download, but here is a list of sites where you can find textures.

2 - Model sources
If you need a model, you can search the internet. On the 3D models page is a list with sources for models. The Google Sketchup Warehouse is a great source to find a torus or a cone.

3 - Horizontal cylinder
Import the vertical cylinder from the 3D models page and rotate it during importing to change its orientation into a horizontal cylinder.

4 - Transparency
Yes, you can make an object transparent if you apply a (semi-)transparent texture to it, like a GIF. Transparency will show black in the preview, and be visible only when using high quality rendering. On some models this works better than on others. On a box the transparent texture will be visible on opposing sides, thus muddying the effect. Use this "box" when you need a one-sided box. On the standard curtain it works fine. Read this to see the effect on walls.

5 - ...
As you can see from my reply, all your questions have already been answered on this forum. Use the search box (top-right), read manuals and tutorials, and use your imagination to try and find answers for yourself before asking them here.

Hans