Well, you can certainly install and run two Windows OSs and a Linux distro without any problems, 'cos I do! No issue in principle why you couldn't have a dozen flavours of Linux happily co-existing, if you've a hard disk big enough, since they can be installed to logical partitions.
As I've just posted elsewhere on this forum, I simply don't get the 'it's too hard' responses that queries about dual-booting Windows and Linux always evoke on this forum. Wake up and smell the coffee, guys and gals, it's really quite easy nowadays! Many modern Linux distros eg LinuxMint12 are 'other OS friendly', because they include the os-prober utility (http://joeyh.name/code/os-prober/) so that all pre-existing OSs are detected and added to GRUB as possible choices.
Alternatively, it is easy enough to choose to install Grub to the root of the newly created Linux partition, mount the Windows partition, 'dd' the linux boot sector to a file called eg linux, then run bcdedit (which isn't hard to understand, run bcdedit /? a few times to learn the syntax) and add that file as a possible boot option to the Windows boot menu. (Then, when you boot Linux, you'll find you can boot back to Windows from the Grub menu, 'cos os-prober has done its work!)
Needless to say, make sure you have a foolproof way of restoring your system to its pre-existing state before you attempt this sort of thing (it's irrelevant whether you're new to it or not, I'm an old hand but always backup first! It's easy to backup/restore the Windows boot aka bcd store before tinkering, using the export/import commands.)
I'll post more details of the specific commands to use if anyone is interested, based on LinuxMint12, and bcdedit on Vista/Seven.