You can of course have Ubuntu and Window$ on the same PC, it's called a "dual-boot". In this case, you have to install first windows and then Ubuntu (because windows erase the master boot record !).
You have 2 possibilities :
1) You prepare a virgin partition before your installation of windows.
2) You install windows on all the hard drive and then Ubuntu will offer you the possibilitie to resize the main partition.
When you'll install Ubuntu, it will install Grub, which is a bootloader. Then when you start your computer, you'll have the choice between the differents OS installed on it.
Friendly,
Franz.
Intel Q6600 Ubuntu 8.10 Alpha 4//Debian Lenny//Gentoo
Sous Linux, 99% des bugs se situent entre le clavier et la chaise de bureau...