I've never had a personal trainer before, but its a good idea.
Another idea to keep yourself motivated is to sign up for some type of sporting event. For example....
The Breast Cancer 3-Day 60 mile walk
The Danskin Women's Triathlon (1/2 mile swim, 12 mile bike ride, 3 mile run)
Both of the above events are absolutely do-able if you give yourself plenty of time to train. I've done the 3-Day and there were women of all ages and sizes walking the 60 miles. I am currently training for the Danskin Triathlon and it's a VERY women friendly & first-time triathlon friendly event. It's designed to be a woman's first triathlon and it's non-competitive.
If you sign up for an event 6 months in advance and then tell all of your friends and family that you're training for a 60 mile charity walk or your first triathlon, you'll be motivated to keep up the training so you can successfully complete the event. Also, you'll feel a great sense of pride and accomplishment when you do complete the event. It's a win-win!!!
You can also ese into this by signing up for a 5K, 10K or 15K race in your area. If you're not up to running right away, many races allow race-walkers.
For me, continually signing up for races and other sporting events is what keeps me on track with my work-outs. If I didn't have something to train for, I would be so tempted to slack off.