I'd go with the second option - safest to keep them as separate as possible. Depends partly on capacity too. If your SSD is a 120GB, two operating systems plus software will be pretty snug. A 250GB drive would give some nice breathing room with two operating systems installed, though I'd still be inclined to have Linux on its own drive.
Keep in mind Linux will need an additional partition for swap space too, although that could go on the hard disk and just use an SSD for the OS itself.
Yeh I could just keep a cheap 64gb ssd and put linux on that I guess.