How can I speed up my Time Machine backups?

You're in luck. I not only use Time Machine, backing up to an Apple Time Capsule (alas, a 500GB unit, not one of the shiny new ones), but I also run Windows 7 within VMware Fusion so I have a very similar configuration to you.

One big difference, however, is that my backups are done over the wifi network so they're even slower than yours, on the assumption that you're plugging in a USB drive and then kicking off Time Machine. Generally I believe that the best backup strategy is one where you don't have to think, don't have to do anything conscious, it just happens automagically. Why? Because I bet you don't back up as often as you used to when you first got everything set up. Am I right?

Anyway, you're right that the presence of VMWare Fusion and similar programs that create massive data files can significantly slow down your backup processing. Have a huge iPhoto library? Working on that next major cinematic blockbuster in Final Cut Pro? Both of those can also create multi-gig data files that require a backup each time they're changed even the slightest.

Fortunately, you can configure Time Machine to skip or exclude these huge data files if you're sure that's what you want to do. Here's how...

Go to Time Machine Preferences from your menu shortcut:

If you don't have that displayed, just go to Apple -> System Preferences... and choose "Time Machine" instead. Either way, you get to the same place:

Look familiar? I hope so!

Click on the "Options..." button in the middle of the screen and you'll see:

Here you can see that I already exclude my "/Applications" and "~/Movies" directories: they're full of huge files that I can always recover or reinstall if worst comes to worst, so I omit them. To add an exclude directory, click on the "+" button...

Find the directory you seek -- for VMWare Fusion it's the "Virtual Machines" folder in "Documents", as you can see -- and click on "Exclude".

That's it, and I just saved myself from doing continual backups of 18.72GB of data. That will speed things up, for sure!

Hope that's helpful. I will again encourage you to think carefully about what you exclude because that's a way of saying "these files aren't important, I can recreate them if my system crashes and I have to rebuild it", which might or might not be true.