positioning tables inside float

[Graham Smith]

I am trying to align a table inside a float, so it sits in the centre of 
the page. I can't see any obvious way of doing this. I thought using the 
center paragraphs might have worked but its greyed out. But that is how 
I thought I had done it in the past

I am using lyx 1.6.5 on Ubuntu 10.04 and lyx 1.6.7 on a Mac running Tiger.
Thanks,

Graham