Weird!
I'll try another browser. I'm using Mozilla Firebird (latest version), which does support iframes and frames, The GIF appears broken, and the properties say this:
The image “http://www.mywebplace.de/mywebplace.de/mathiaspohl/iframe.nsf/loading.html/ls2004” cannot be displayed, because it contains errors.
Useful message from Firebird eh?
Update: works in -- gasp! -- IE 6 ;-)
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http://www.benpoole.com