the drive from San Francisco to South Lake Tahoe and State line can be via the US Route 50 East which takes about 190 miles and 3 1/2 hours or you can take the longer but more safer route via Interstate 80 East up the Donner Summit then turn right to Highway 89 in Truckee and then Past Tahoe City, along the Western Shores of Lake Tahoe for a longer 230 miles (about 4 hours). both routes converge at Sacramento and either route you take is driving along winding roads and hairpin curves and wonderful views.
When driving to Tahoe in the Winter time, unless you have a 4 wheel drive vehicle WITH SNOW TIRES, you should charry tire-chains with you. There are often chain check-points where police will make sure you've got chains on your car (or have them with you, if the need is predicted). If chains are required and you don't have them, you WILL be turned around and told to go buy chains or go home.
Trying to hire a car in Sacramento was not easy. The first 3 places I tried had nothing available for that day. I wondered if I should have to stay in the city, and not get to the Lake. A bus driver I spoke to thought that the Greyhound service ran to South Lake Tahoe, so here was another option. However, I haven't been able to find any such route on the Greyhound site. The nearest I could come up with was from Sacramento to Carson City, in Nevada, and some miles from the Lake. The actual distance of that route being 136 miles. And the single fare is (1 Jul 03) $37.50. So, my hire car at $32 (plus gas of course), was much more economic. The Greyhound service to Carson City (not really that close to South Lake Tahoe!), takes 6 and a half hours. By car it takes about 3 hours for the 100 or so miles.
The best scenic route, but one you'll want to avoid in bad weather is to fly into Sacramento, CA and take the Interstate up through the Sierras and into South Lake Tahoe. The trip from the Nevada side is decent but doesn't compare to the drive alonside the American River.
You'll need a rental car because there the drive is wonderful around the lake. Plus the mass transit system won't get you to must see sites outside of town.