As I am stumbling through Facebook App Dev. I am getting more and more close to a bit sophisticated questions, bu still I am at newbie level.
Can I have custom Tab and inside that tab two different apps ? ex. (the slideshow and top 5 news(RSS feed))
No you can not. But - if you create your own application you can include a slideshow and an rss feed into the same application and have that in your custom tab.