With Blog City, you can very easily add HTML/Javascript code to the gutters or header of your blog. This can be any kind of code, for images, google adsense, blog-rings, paypal buttons, weather pixies or hit monitors. To do so, log into your blog administration and go to the Widget menu tab.
From there select one of the 4 widget areas (default is Main blog). Your html/javascript may need to be in the gutter, it may need to be in the header, just click the add widget icon to move forward. This will pop up the Widget Browser.
Please choose the General tab and choose the html snippet

Either type or paste the code you want to use here, and click Ok to save.

Using the 3rd tab along, you can Preview your javascript or HTML (although bare in mind some javascript doesnt produce an output you can see).