The amount of rest you need will depend mostly on a few different factors:
1) Workout Intensity. If you're doing relatively light weights for a higher number of reps, your recovery time will be greatly reduced over a routine that has you hoisting heavy weights with maximum intensity for lower amount of reps. It's isn't uncommon for someone training very heavy and using high intensity to only work a body part once a week.
2) Amount of sleep / quality of sleep. When you sleep is when your body repairs and rebuilds itself. If you're cutting your sleep short, you're cutting your body's ability to recooperate short.
3) Nutrition. Eating a diet of quality foods will help shorten your recovery time. Pay special attention to getting enough protein for muscle repair from high quality, low fat sources. Chicken, fish, and turkey are great. A multi-vitamin is a good idea too. If you lack one nutrient, it can short curcuit the whole process.
A good basic split that I enjoy is day 1, Chest, shoulders, and triceps. Day 2 is back and biceps. Day 3 is legs, and day 4 is rest, then repeat the whole process over again. If your workouts have to fit nicely into a 7 day schedule, what you can do it compact it a bit. Day 1 would be chest, shoulders, triceps, and ****s, day 2 would be back, biceps, and hamstrings, and rest on day 3. Day 4 repeats day 1, day 5 repeats day 2, and rest on days 6 and 7 (or go riding!).
J&K