I want to make my gtk2 theme for KDE.
Is there a good instructions/tutorials/tools for creating a QtCurve theme. Can Images be used as elements (buttons, badgrounds, handles, scrollbars...)
Your question is a bit strange, since QtCurve is a Qt/KDE theme already.
If you want to build your own theme based on that, the easiest thing to do is to download its source from kde-look.org, start by building it without modifications to make sure you've got that part right, then start changing things progressively.
If you want to write a Qt style yourself (those are written in C++), you should take a look at the Qt Style Plugin examples. (This isn't trivial. Also have a look at Qt Stylesheets while you're at it, and Qt Styles and Style Aware Widgets.)
An alternative to this is to use QuantumStyle which you can use to create SVG-based styles without requiring C++ code.
For Plasma themes, you should head over to TechBase and read the Creating a Plasma Theme in 7 Easy Steps guide.
For custom KWin decorations, you should have a look at KWin decorators part of the KWin Hacking page, which links to a few options (deKorator, AuroreaDesigner and Smaragd). The other option is again C++, and a HOWTO is also linked there (but it's out of date, the other options are most likely better these days anyway).
QtCurve is a theme engine, not a theme in and of itself, although it does come with a default set of themes. The themes are just text files that define how you want each component to look, e.g., the scroll bar, etc. If you go to the KDE settings page for Application Appearance -> Style, you can see if QtCurve is installed by seeing if it is listed in the drop-down box near the top of the window, labeled "widget style". If not, install it via apt-get or whatever. Once it is installed and appears in the Style drop down box, select it, then click the "configure" button to the right of the drop down. In the window that appears, you can either choose a theme to start with or just begin modifying the current theme (named "current"). On the left side of the window, there is a large array of choices to choose from, where you can change everything about your selected theme. It is a bit cumbersome to see your changes, as you need to keep clicking the top-most item "preview" to inspect your changes and see if they are too your liking. I sure wish there was an instant preview box that keeps being updated as you change things, but not yet. In any case, when you are satisfied, select "Save" just below the "presets" drop down box near the top of the window, and select a new name for your masterpiece. :) QTcurve is surprisingly configurable. The text files end up getting deposited in: ~.kde/share/apps/QtCurve, but you can use the "export" button to save off your work for backup. Importing is similar, using the included "import" button.