As far as setting up a Windows and Ubuntu dual-boot is concerned, it's easy. Just install Windows first, then when you come to install Ubuntu you can choose which drive to install it and set-up multi-boots etc really easily.
As for where to install the OS's, both Windows 7 and Ubuntu run well on SSDs. If you have a 128GB drive and you want both OSes to take advantage of the SSD, do a 64GB/64GB split. If you're not fussed about speed, then put one on the SSD and one on the 2TB drive.
How many programs are you going to run on each OS? At the moment with Windows 7 Pro and stuff like Visual Studio, Adobe Master Suite and games all loaded onto my SSD I have around 30GB of free space. If you're going to install loads of stuff on one then you want the most space possible.
Hope this helps?