I'm going to be in that boat next year. I'm getting married this summer and then starting at ICO in the fall. I have asked a few people about this and have received a few pointers.
1. Make it clear to your spouce that for the next 4 years school is a very big part of every aspect of your life. They truely need to understand this. My soon to be wife is very conscious of this fact and has taken up a few "quite" hobbies; eg. knitting. I make fun of her because when she sits there she looks old, but I appreciate the effort she is putting toward my efforts.
2. On the same note, despite the stress of graduate school, make it a point to set aside time for eachother. One of my tour guides at ICO is married and said he and his wife set aside Friday night as a time together no matter what else is going on. I hope to have time to do this as well, but I have made the promise that I will eat dinner with her every night (except the clear exceptions when one of us is gone or has a meeting or other extreme situations).
The divorce rate among medical students (MD, DO, DDS, OD, DPM) is very high, above the national average of ~50%. It is a gamble, but if you are suppose to be together, you will make it.