the solution i've got is kinda awkward IMO but here it is:
after you're done typing the entry, check "edit html" and add
to the beginning of your entry
and then
to the end of it.
watch out when you're editing the entries, from my experience, xanga likes to mess around with the HTML when you're switching between "edit HTML" mode and regular mode.
and um, i know sorry if createblog.com doesn't like it, but i think this solution is too trivial for the little "provided by createblog.com" tags on it. kinda clutters up the textbox, if you'd ask me. I guess you could remove it, and leave some little note in your custom header area that you found the code on createblog.com.