Icon Sets
The Default Icon Sets
By default, Trinity ships with one icon set (Crystal SVG) in tdebase, five more (iKons, KDE-Classic, Kids, KDE-Locolor, Slick Icons) in tdeartwork, and one (Monochrome) in tdeaccessibility. Here's a quick comparison chart (using the largest folder icon available as a visual sample):
| Name | Creator | Largest Size | Sample | Notes |
|---|---|---|---|---|
| Crystal SVG | Everaldo Coelho | No max | 
|
The KDE3 default icon set (and Trinity's as well, since we haven't replaced it). Infinitely resizable .svg icons. |
| iKons | Kristof Borrey | 64 x 64 | 
|
Most icons are only available at sizes up to 48 x 48. |
| KDE-Classic | Torsten Rahn | 64 x 64 | 
|
This was the default KDE3 icon set prior to the introduction of Crystal. Most icons are only available at sizes up to 48 x 48. |
| KDE-Locolor | ??? | 32 x 32 | 
|
Similar to KDE-Classic, but with fewer colours per icon. |
| Kids | Everaldo Coelho | 64 x 64 | 
|
|
| Monochrome | Danny Allen | No max | 
|
Black-and-white icon set for monochrome/low-colour displays. Infinitely resizable .svg icons. |
| Slick Icons | ??? | 64 x 64 | 
|
Using Non-Trinity Icons with Trinity
Go right ahead. Trinity should be able to use any icon theme suitable for X Windows desktop environments, including icon themes for KDE, the various custom icon themes created by Ubuntu, themes created for Gnome, etc.
Once installed, additional icon themes should show up in the Control Center under Appearance and Themes > Icons.
OpenDesktop
If you don't like any of the sets your distribution makes available, the best place to look for additional ones is OpenDesktop and its child websites (like KDE Store). Icon sets for KDE will probably have the largest selection of icons for Trinity-specific applications like amaroK and Konqueror.
There you can even find icon themes adapted with Trinity in mind. For example, francescobat's extensive Trinity Desktop Collections.
Custom icon themes
If you want to pick and choose individual icons, they can be in .png or .svg format. Microsoft Windows .ico files won't work, but you can convert them to .png by using appropriate software.
If you want to create your own icons, you can use your preferred raster or vector editor. You could also have a look at the tdeiconedit application, found in the tdegraphics package.