After the installation I experienced two problems:
1 Images of the template were not suited for high resolution screens
2 I could not install the jvse JoomSEF plugin (my mistake)
The first problem was fixed within short notice by jv-extensions. They mailed me a new set of images, which I installed on the webserver, and the problem was fixed. The second problem was my own mistake. I tried to install the jvse Joomsef with the general Joomla installer, which is not correct. Instead, try the following steps:
1 Make sure joomla 1.5.x is running in legacy mode
2 Install JoomSEF 3.2
3 Go to the backend and click on the JoomSEF module, next click on install (top right) and select the ext_jvse_v100_j15xL zipfile.
In sum, the module has many advanced features, at least everything I need. Moreover, the biggest advantage of choosing a JV-extension is the great service! They respond quickly, are patient and have a lot of technical expertise.