Hi Len!
You can try this and see if it helps.
Open iPhoto > select photo to be printed... iPhoto > File > Page Setup, make sure you have your printer selected and you should be able to select borderless 4 x 6 as a paper size (if in UK you can try A6 but that's slightly smaller than 4 x 6) and make sure you select correct orientation. Hit OK (I think this is the most important step)
Now go to Share > Print, make sure your printer is selected, from here click on ADVANCE button, again make sure correct printer is selected, go to "Paper Handling", select "Scale to fit paper size", it shoud list 4 x 6 borderless, UNCHECK "Scale down only". At this point you're done telling iPhoto you want a borderless 4 x 6
From here you need to select Paper Type & Quality and Borderless from the drop down menu (depending on type of printer this may vary slightly but it should be there)
Now hit PREVIEW button and see if it looks right - Print (if not hit cancel and start again, you can print a borderless 4 x6)
Good luck, after the first few it gets much easier
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
As a caveat, this will work as long as your printer is capable of printing 4 x 6 borderless photos, which most are ...(-: