Joomla is installed 1.51 into not main directory but in folder

All directories I even chmoded to 777 (was 755)

Joomla 1.50
PHP 4.4.9
Apache
mySQL < 4.1.2

if you google your error you see it has all to do with rights on directories, so I suspect it has nothing in particular to do with the itemtype image-gallery . Can you try to install another component just to see if that works?
Which Joomla version are you using?

I tried to install in J 1.50, - unusuccesfuly you think, because it is in folder. I tried this for my experimental website.

Ok, I will try in other website with J1.56 and in the root - already installed successfuly, now need to learn how to work

But I can't find how to do Gallery. I need to show a couple schemes, I enabled plugin and Top menu
but where to create Gallery?

www.archeonas.lt
Click on "Genealogines schemos"

so you installed Pages-and-Items and Images-gallery on Joomla 1.5.6, you enabled in Pages-and-Items configuration the itemtype 'image gallery'.
- go to components > Pages-and-Items. In the left column you see all the pages of your website, probably under 'mainmenu'. click on 'open all' to see the whole structure of your site.
- click on the page which you want the image-gallery on. If the page is not there yet, click 'page new', fill in a title and click 'apply'.
- under 'items on this page' select 'image gallery'.
- click on 'new item'.
- fill in title.
- click 'apply' to save the new item.
- click 'add new image'.
- select an image and click 'save'. Do that for as many images as you like.

You need to have installed the Pages-and-Items plugin and enabled it for it to process this itemtype.