Possible Duplicate:
How do I set up a dual boot Windows and Ubuntu?
Dual booting Windows and Ubuntu
I am building a computer and would like to dual boot these two OS's
Possible Duplicate:
How do I set up a dual boot Windows and Ubuntu?
Dual booting Windows and Ubuntu
I am building a computer and would like to dual boot these two OS's
Install Windows 7 first, then once that's installed and set up you can insert your Ubuntu LiveCd and boot from it. The Ubuntu installer will detect the Windows 7 installation and give you the option to install alongside it.
This is just a brief description, if you need help with the installation processes for either Windows 7 or Ubuntu there's plenty of guides online.