DataGrid displays differently on NT4 vs XP

I built a WinForms c#.Net application on XP. When installing on NT4
horizontal scrollbars appear in some of the datagrids that did not in
XP. This is really messing up the appearance of my application. I
tried different resolutions on the NT machine and received the same
result regardless.

Is there a way to tell the maximum width available before the
horizontal scrollbar appears so I can make the columns "autosize"?

I know I can determine the OS at runtime and format it differently but
figuring out the maximum width manually for each datagrid will be very
time consuming.

How do you generally handle display differences between OS versions?

Thanks!