On 2007 it's by going into the DocLib settings and turning on management of
content types in the advanced settings. Then you go back to the settings page
and can edit the button order of the 'New' button. You can set whichever one you
want to be the default.

Yep, that doesn't work in 2010 for some reason, at least not on publishing sites
with infopath forms. It should be so easy to get a new infopath for to pull up,
instead as it turns out it is easier for me to pull my hair out, what is left of
it anyway...

office.microsoft.com/.../add-an-existing-content-type-to-a-list-or\
-library-HA010378235.aspx

Change the New button order or default content type

You can specify the order in which content types are displayed on the New button
for a list or library. By default, the first content type that is displayed on
the New button becomes the default content type for the list or library. To
change the default content type for the list or library, change the content type
that is displayed first on the New button. You can also specify whether you want
content types that have been added to a list or library to be visible on the New
button.

If the list or library for which you want to change a content type is not
already open, click its name under Lists or Documents on the Quick Launch.
On the ribbon, do one of the following:
If you are working in a list, click List Settings.
If you are working in a document library, click Library Settings.
Under Content Types, click Change new button order and default content type.
NOTE If the list or library is not set up to allow multiple content types,
the Content Types section does not appear on the Customize page for the list or
library.

In the Content Type Order section, do either of the following:
To remove a content type from the New button for the list or library, clear the
Visible check box (this check box is selected by default).
To change the order in which a content type appears on the New button, click the
arrow next to that content type in the Position from Top column, and then select
the order number that you want.