similar camera , similar performance ?????

have been having a look around for something to replace my Canon G2 - more
zoom primary and a bit more MP (secondarily)
I have 3 x lenses (28-70,35-80-100-300) to suit my Penatx Z-70 so the Pentax
*ist looks quite good value althought its seems its getting trickier to get

I'm looking at some filters on B&H, and I've come across (what seems
like!) a cool toy that would improve macro photography.  Would this
fit, using the adapter tube?
http://www.bhphotovideo ...

Do they exist? Do they work well? and are they expensive?  Am on pokey
dial-up and so far have not found much information.  It was because of
newsgroup information that I got the FZ5 .... needed something good and
lightweight.  I would be grateful for any information....