Windows Parition on External Hard Drive... with complications

Hello experts out there. I thank you in advance for your help. I have a MacBook Air Mid 2011 with 1.6 GHz Intel Core i5 processor, and memory 2 GB 1333 MHz DDR3 memory. I also have a 100 GB WD external hard drive I am currently using to back up my files on my Mac through time machine. From a previous computer I also have a copy of windows 7 home premium from a previous computer. My ultimate goal is to partition the external hard drive into three parts...

1) The first partition I would like to use an additional storage for my Mac

2) The second partition I would like to use to back up my Mac

3) The third partition I would like to use to run Windows so that I can play some of the old games I loved as a kid (roller coaster tycoon, a bridge too far, etc.)

If anyone has any idea how to download some of the old Close Combat: A Bridge Too Far Games for Mac that would certainly make this situation less complicated. However, in lieu of that working I would love some help making the above paritions happen. Thanks again and I would be happy to provide anymore information if that would make this easier.

mpz34