I've got a 3.5" card reader that goes into a floppy drive slot but i would like it in one of the drive slots below the cd rom drives, what is the thing called that you can buy to mount it in one of those bays, it's like a 5.25" mounting thing.

You mean something like this? (http://www.maplin.co.uk/Module.aspx?ModuleNo=36414&doy=21m5&C=SO&U=strat15)

Yes :) but obviously 3.5" to 5.25" and not the other way around...

Maplins don't appear to sell the 3.5" to 5.25" :(

you have a 5.25 bay that you want to turn to 3.5 ? thats what the adaptor the other poster has posted does ?

No I have a 3.5" card reader and i want it transformed into a 5.25"

You need the adaptor I said surely?

Put the card reader into the 3.5" space on the adaptor and then put the adaptor into the 5.25 drive space. Et voila card reader fixed to 5.25" drive space?

That is the correct adaptor