When I was pregnant with my twin daughters, I was first ordered to limit my activities at five months, and when that didn't stop me from dialating I was put on bed rest. I spent about two months in bed, and they let me get up when the babies reached five pounds each, about a month before they were due. (Please note that twins are usually ready to be born at a lighter weight than singletons.) My twins were born naturally less than a week after they let me get up, so I guess they knew what they were talking about. They were small but healthy, and were able to leave the hospital on a normal schedule. (After three days, which is normal for twins.)
In contrast, I met a woman once who had twins who said they wanted her to go on bedrest, but she said didn't have time. I asked how the babies had come out, and it turned out one had to be in an incubator for months and had problems that took years of therapy before the child was "just about normal." The couple of months in bed could have saved so much time in hospital visits, doctors appointments and therapy, not to mention that the child may have started life at a normal weight and avoided some of the problems that can come with premature birth.
They have developed more and better methods to care for premies, but to me, having my child(ren) bearing a full-weight child is the best choice. My advice is to follow your doctor's advice. If there is any way possible, stay in bed. If you can get regular massages it makes you much more comfortable. Also come up with an exercise routine with lots of stretching that you can do lying down and ask your doctor if it is OK. Get friends to bring you books, eat lots of salads and be aware that it is easy to gain extra weight on bedrest. Elevate your feet, and switch positions frequently. Make it a time to learn about parenting with books, tapes, DVD's. Catch-up on watching movies that you have missed. Most of all, know that what you are doing will help your child and is an act of love.