Here is my method:
1. Download SUN VIRTUALBOX
2. (INstall...) (INstall a copy of windows XP (TinyXP in BARE configuration, with IE, WMP and driver packs.... Preferred.)
3. Make a few copies of the hard drive file, use the copies to quickly set up a few additional "Boxes" (Select as hard drive file, rather than create)
4. Each box should have 128MB of vram and ~386MB of regular RAM dedicated to it.
5. use IE advanced network settings to set up the system through a proxy
6. Bot on this "Unique" Computer that appears unrelated to the others you are using :s
7... Profit?
Uhm, fill in the blanks with tutorials (Google) that actually cover how to use virtualbox, install windows XP, setup computer wide proxies, etc.
(I Dont have the time to explain all of that, just the overview.)

