If you need to display text exactly like it is typed (without any formatting), enclose the area either with <nowiki> tags or even simpler, with double percent signs %%.

This is some text which contains addresses like this: http://www.splitbrain.org and **formatting**, but nothing is done with it. The same is true for //__this__ text// with a smiley ;-).

<nowiki>
This is some text which contains addresses like this: http://www.splitbrain.org and **formatting**, but nothing is done with it.
</nowiki>
The same is true for %%//__this__ text// with a smiley ;-)%%.