Hi there!
I've got a wide format HP as well as an Epson 620, I normally print out of Photoshop, but your question got me curious.
Here's how I did it, Open iPhoto > File Menu > Page Setup > you should have an option for "Borderless Super B" ( or your choice of paper size), this is the important step
Now select your image to print > Share > Print > Advance > from here look for selection to, "Paper Handling" > look for "Destination Paper Size", I selected "Scale to fit Paper Size:" and then find "borderless super B" > and to make sure it looks OK, hit Preview > you should see your print preview and it should be Borderless... and like magic it worked and I did print a borderless 13 x 19 through iPhoto for the first time!!!!! WOW!
*If it doesn't look right in the print preview, hit cancel and start all over, it's there, you just need to find the little things that will make it happen...
Good luck, Rick
iMac G5 iSight 20" - 30G iPOD & Hot Pink Nano 4G - WD 500G FW - Mac OS X (10.4.8) - HP Pav 15" WS and Toshiba Sat 17" WS LP's - Canon 20D & A620 Kodak P880
Message was edited by: JMEH
You're from the UK, so there may be some small differences as far as Super B v B3 v B3+ across the pond... I think you know what I mean