I certainly don't consider myself an expert in html writing, but I do have a handle on a few things. A couple of people have commented on the Halloween background, so I thought I'd post a short tutorial on how to change a background.
First, you'll need a picture. I found some good ones on Hellas Multi Media-- but beware, this site has a billion very annoying pop-ups. Once you find a background image that you like, right click on it and save it somewhere you can find it.
Next, you need to upload to blogger. I do this by creating a post and uploading a picture, but instead of publishing the post, I select "Save as Draft." That way you don't have a post with a weird background picture. Now that your picture has been uploaded, you'll want to select and copy the http:// on to get the picture's address on blogger.
Now, open your Blog template. In the first few lines, you should see a tag for the background. It will say something like Background: or background=. If the tag says background with a colon after it, you'll want it to look like this:
background:url(http://paste the picture's address here)
If the tag has an equal sign, it should look like this:
body background="http://paste the picture's address here"
Once you've done this, you can select "Preview" to see if it worked. If so, save your changes and re-publish. If not, you can clear the edits without messing up your current blog.
Hope this helps-- Good luck!