My son just turned 7 months old and from the reading I've done, babies around 5-8 months typically nap at least an hour in the morning (around 9am or 2 hours after waking) and then take a longer nap, about 2+ hours, in the afternoon (at about 1p). Consider pickig up a copy of Healthy Sleep Habits, Happy Child by Marc Weissbluth. It helped me understand how a baby's natural biorhythms influence the time of day he/she will tend to feel tired, etc.
Also, at your son's age, you might check to see if he is teething... that discomfort can definitely disrupt sleep. Try Hyland's Teething Tablets -- I've used them with both my children with great success.
And finally, try giving your son a super soft or silky blanket to hold when he's going down for his naps. I call both my kids "blanket babies" because they just fall asleep so much easier when they've got their blankets to rub against their faces. It's sort of a ritual for both of them -- but only at rest times... nothing like Linus, so don't worry about your son creating an unhealthy attachment :0)
One last comment -- avoid ever starting the habit/expectation that sleep time must happen in a quiet, dark room. I know a woman who had "blackout" blinds on her son's windows, and now he is so programmed to have complete dark when he sleeps, that he cannot nap anywhere away from home. Don't let that happen to you...
Best of luck!