As long as you have space it should be no problem but you would probably need to shrink the windows partition to give room. As you already have a dual boot system you will know about shrinking the windows partition and it should be relatively straight forward. The important point, apart from backing up your work, is to choose custom partitioning during the install and set one or two partitions for Sabayon. The installation should give a grub boot screen that will allow you to choose between the three systems when you boot up.
Running the live DVD before the installation should show if there is going to be a graphics problem.
Best of luck - I hope you can join us.