Drove there once few years back, journey is about 3 hours depending on how fast you are driving, nothing much to see in Malacca. I can't really remember how to get there, all depends on the map and road signs. Also drove up to Penang Island once, took me 11 hours cos rested a few times & stopping for meals, feels that Penang is still best!
I drove from Singapore to Malacca a few times. The journey takes about 2.5hrs - 3hrs. There is nothing much to see on the highway. (mind you, the North-South Highway is not cheap.) You just follow the road sign and you will arrive in Malacca with no problem.
Once you arrive in Malacca, head straight to the "old quarter", where they have those old red coloniel buildings, old shop houses and clock tower. You can take some nice sunset photos as well.
(another mind you, there are recently a few cases of cars being stolen in Malacca, mostly Singapore-reg cars.)
Sunday-earlymorning-till-night is possible. 2-3 hours up and 2-3 hours down (from JB) depending how fast you drive. Exit at Ayer Keroh, Melaka. Good to have another driver with you if you're not used to long distance.
Usual places to visit and shoot - Chinatown (nice narrowly long colonial buildings unique to chinese community, old temples), Sultanate Palace, Sam Poh (Cheng Ho) Temple (at Bukit China where Chinese Princess once lived IIRC), Portuguese fort and Dutch buildings. Melaka Town is not very big, they are even reclaiming land there (Makota area). A lot more peaceful than Penang and KL, people are generally very friendly.
Agree with Digipix that sights in Penang are better (perhaps the long drive makes you appreciate the city more), but food is better in Melaka Drove up to Penang twice with stopover in KL. Nice places to visit along the way too. Aiming for Perlis, Kedah, Thailand (read that driving there is more cumbersome than in M'sia, needs to pay import tax for car even for holiday visit etc.) and East Coast next time.