If you want Ubuntu to install without taking over the boot from Windows, make sure you click the "advanced" button during the boot manager stage. This brings up another menu which gives you the option to install grub to the Linux partition, not the MBR.
Then in W7 use easyBCD 2.0 to add a linux entry to the W7 BCD. Your W7 will continue to boot as default, with an option to use Linux if you need it.
"Why would I need it " ? I hear you ask
Jake will tell you it's better than Windows, but as a long-term Windows-app user, with most of my daily routines running on Windows dependent software, I know that it's not a simple task to rewrite your Lotus 123 stuff in Open-Office when it's a gigantic complex app.
My reason for having it available is simple. If you've ever tried manipulating anything in WIndows manually, you'll have fallen foul of Windows UAC, permissions, controls, ownerships etc, which prevent you from doing the simplest of 1-byte edits without jumping through so many hoops, and doing so much research about how to alter permissions, take ownership etc. etc. that you'll probably give up in frustration before you succeed.
Even if you're trying to alter something in a dormant XP or W7 from Vista, you'll still hit the same problems.
However, boot up Linux and you can merrily scythe your way through the Windows files because it simply doesn't care what restrictions MS has handcuffed you with.