svetoslavm:
I've had a look on the page, I have focused only on the section you mentioned but the page structure is still messy and if it was me I would start it all again from scratch, it could take you a much longer time to repair than to start a clean layout.
I've noticed in the page source that there are 9+ css files, it also returns 300+ errors when validated against
W3 validator you can view the validation results
here.
Before you start using jQuery you should have a clean validated document and css, I'm aware that CMS solutions such as Modo CMS etc.. makes it very difficult to obtain a valid document but one should note that jQuery requires a valid document to function properly and it also minimizes cross-browser compatibility issues.
However, I don't think the validation is the problem here, but it's the way the Page is constructed and CSS, there seems to be a lot of positioning (relative, absolute, static) even without the slideshow script and the more absolute position the more problems you're going to face.
For the slideshow you will need to give the slideshow container's class a width and height that would fit the images inside, since they're absolute positioned due to layering.
Modifying you
.slideshow class as below will fix it for you but I still believe that further work would be required.
I hope I have helped in any way
Best of luck
