...change your display performane in indesign, view > display performance > high quality...
...the trouble with pasting excel charts into indesign is they are RGB colours which isn't ideal for high end graphics output through postscript RIPs...
...you can perform a color conversion when exported to PDF or printing to postscript, based on your color settings destination profile, the source space used for pasted excel charts is your RGB working color space...
...the resulting chart will be vector based, although made up of far more vector points than is really needed to create curves, that is just the way excel draws charts...
...for better charts print to pdf from excel...
...another method would be to paste it into photoshop and change it to cmyk there in a high resolution document. When you create a new doc in photoshop it will take on the dimensions of the copied excel chart from the pasteboard data, the edges will still be a bit rough though...
...if you need a bigger chart than excel offers you will be better off resizing a placed pdf in indesign as opposed to using copy and paste or photoshop and resampling...
...ensure you have 'high quality' selected in the page setup of excel before you print (or if you really have to copy and paste from excel)...
...the best option is to create a pdf from excel of you pie chart and place this in indesign or if required you can rasterize it in photoshop and change to cmyk there, rasterize to something like 300 to 600dpi for a much better result than copy and pasting...
...avoid copy and pasting into DTP applications in short..
Andrew