Making Ubuntu the default OS in Windows Boot Manager

If it helps, I believe I installed Ubuntu inside of Windows via Wubi.

Sagar, I think this issue is BCD(Boot Configuration Data Editor) which is in Windows Vista. I am not a tech guy of UBUNTU, Though I worked on XP which you're expecting it to work on the sequence of booting to be change. And presently your system is using Windows boot loader, hence, you can do that in VISTA itself.

this link will let you know what I am talking about and even gives you solution for it

http://technet.microsoft.com/en-us/library/cc721886%28WS.10%29.aspx
I found the same solution mentioned below..
Startup and recovery. The Startup and recovery dialog box enables you to select the default operating system to start if you have multiple operating systems installed on your computer. You can also change the time-out value. These settings are located on the Advanced tab in the System Properties dialog box.

Its you still won't get
Try this link which shows you how to do with commands. In you must do the DISPLAY ORDER COMMAND..
Check the below link.
http://www.flexbeta.net/forums/index.php?showtopic=8373

To know how it looks in your vista
Check this link. try to make change in displayorder

http://www.windows7home.net/how-to-use-bcdedit-in-windows-7/

Try it, may work.

http://www.lytebyte.com/2009/02/05/how-to-change-the-default-os-boot-order-between-windows-7-and-vista/

This is what I'm talking about

Thank you for your help! I'll try this.