Warning:This can make your PC an Unbootable mess causing you to have to repair grub. But this is generally a safe edit.
Open a terminal then type
Sudo gedit /boot/grub/menu.lst
It should ask for your password and then open menu.lst in gedit. In the file there should be a line that says "default=0" (or whatever the default is set to). Now scroll down to where the different boot options are and count (starting at 0) the number of entries until you reach the Windows entry. edit the "default=" line to that number.
Handy list of grub commands
http://www.gnu.org/software/grub/manual/grub.html#default
Moving on to the Custom resolution (see warning above) assuming your monitor and graphics card (and the linux driver) can handle the resolution
Open a terminal and type
sudo gedit /etc/X11/xorg.conf
yet again Ubuntu will ask for your password and then gedit will open the xorg.conf file. Find the Display subsection in the file it will look like this
Section "Screen"
Identifier "Primary Screen"
Device "ATI Technologies, Inc. M22 [Radeon Mobility M300]"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1280x1024" "1024x768" "640x480"
EndSubSection
EndSection
add your resolution to the list of "modes" (notice the other resolutions are in quotation marks, make sure your custom one is too)