then i go to my blank basic page in showkase and i add that line: <embed src="index.hmtl"> then i click on source, the line gets grey with weird symbols, i save, publish but the text shows up on the page but not the tour...
You need to click on 'Source' (to enter 'Source' mode) before entering your any HTML code (not afterwards).
Whatever software you use to create your virtual tour, please check with their support to see if they have any information on how to embed their virtual tours into web pages.
If you are trying to add the code <embed src="index.html"> to your Showkase page, then I expect the virtual tour is somehow embedded into the 'index.html' file. You could open the 'index.html' file in a plain text editor and examine the code. If you find the code which embeds the virtual tour into the web page, you could copy it into your Showkase page (being sure to click 'Source' first). If the virtual tour comprises many files, then you may need to ensure that they are uploaded to the correct location on your web server and that the paths in the code you use are correct.
Otherwise, you could certainly load the 'index.html' file into an iframe by using code such as:
<iframe src="index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
I hope this helps.