windows 7 is pretty easy to run 2 os's on IF you install from scratch, I used to do win xp and win vista/7. Just install linux first, then win vista/7 and it should set it all up for you. If you've already got windows installed it's a little more complicated.
Most linux distro's usually come with built in software to allow for dual operating systems, 99.9% certain ubuntu does,
If you're adding a second windows os (think xp and win 7 like I did) and you've already got win 7 installed you can get a windows program called easybcd that can change or add the boot loader when loading. You need to install the second windows os first. This should work with a linux partition too but I've never tried it and you may have issues getting into the windows os.
If you just need to partition a drive, you can do it in windows by going to 'administrative tools' and then finding 'computer management' (you can just type this at start in win 7/vista). Once there click on 'storage' followed by 'disk management' and then select the drive you want to partition.
You've got the option of full partition for a fully clean drive with nothing on it or if you need to shrink a partition you can select shrink (extend if you want larger).
Note: I have not tried the shrink/extend so don't blame me if this messes up - it shouldn't but you never know.