can anyone please tell me where i am being completely stupid!
Well, not meaning to be rude, but... Using ID to create screen graphics might qualify. You simply have no way of controlling pixel grid alignment, which is what bites you here. ID's preview is just that - the document rasterized to the current screen view and as soon as something is placed on a fractional value you get the antialiasing. You seriously need to move on to PS or AI - export your current stuff as a high-quality vector PDF and do any iconification in one of the two other programs based on your PDF opened/ imported there.
Thank you for assisting..... I am using the icons for web. I have saved the vectors out in illustrator and photoshop with not much difference in quality. 72 dpi png & jpeg!