A quick check on the Sandisk web site's Compatibility checker lists their 16Gb cards as compatible with both D200 and 400D. Of course it does not say whether the cameras can see all 16Gb!
Mind you the price you quote is indeed very good for a 16Gb card and in the typical range for an 8Mb card ...
I would be tempted to try it in the Canon and see what capacity the 400D reports for it.
If it says 8Mb, send it back OR try it in a card reader and see what the PC thinks it offers.
On the other hand there are some interesting comments here but skip the first half of them ...
http://www.flickr.com/groups/d200/discu ... 880157864/