To disable decimals on quantities you can add the following validation control in the productlist.ascx and cart.ascx pages:
<td>
<asp:TextBox ID="txtQuantity" Width="50px" MaxLength="4" CssClass="SmithProdText" runat="server" Text="1"/>
<asp:CompareValidator ID="cvQuantity" runat="server" ErrorMessage="Enter a whole number" ControlToValidate="txtQuantity" Operator="DataTypeCheck" Type="Integer"/>
</td>
I will send this into programming to create a BuyNow module setting to disable it and it will be available in the next version.
Thanks,
Scott