Check this out-- According to Nitix, Nitix on Linux outperforms almost 17x Microsoft Windows Small Business Server 2003 in a test case comparing the Installation of the Operating System and Core IT services!
And, here are more details of a product performance bakeoff done by CRN:
"Net Integration's Nitix Linux small-business server offering packs every bit of the feature punch of Microsoft's just-launched Small Business Server 2003 R2 ..."
Try Nitix with IBM Lotus Domino at no cost here: http://www.nitix.com/products/domino/requestDownload.php.
They already have Sage Accpak running on Nitix: http://www.nitix.com/products/accpac/index.php