Hi,as already said the biggest limitation her is time.Personally i made good experiences with interpolating images in photoshop.Use a smaller rendersize with 300 dpi resolution at final settings and render it to disk.Up to 60 % interpolation you don`t see any difference when you interpolate them in photoshop.To get more on the safer side you can even use a bigger resolution if you want to. In my case i make photoprints at 300 dpi up to 24 " wide. cheers rollmops :-)

http://www.fredivoss.de 

...yippi ah yeah or something like that...