Serious Eats - seriouseats.com

Oh wow. Where to start? Try Eliot Coleman's New Organic Grower, get yourself an organic gardening encyclopedia, and as for seeds, try Seeds of Change, the Seed Savers Exchange or this great site for Italian heirloom varieties.

I often use Johnny's Selective Seeds.
http://www.johnnyseeds.com/
They have great heirloom seeds. I have been using them since 1990.
Also for gardening forums with gardening information by zone try Gardenweb.
http://www.gardenweb.com/
a great gardening community I have used since 2002.

Another vote for gardenweb. I've learned a lot from people who have been gardening for forever.

You say "taking care of" the garden - like garden-sitting? A temporary thing? If so, your first and most important source should get be instructions from the current gardener. Inventory the tools, water sources, and compost piles. Make a map of the plantings, if you can. You will want to learn about the general needs of your plants - water, sun, fertilizing, pruning, etc. Ask about bugs and signs of disease for your plants. Know what pests to watch for in your area - deer, raccoons, neighbor children, etc.

Rather than try to learn everything about gardening, try handling problems as they arise, and GardenWeb is a great place to start. Another fabulous source is your state's Agricultural Extension program, usually affiliated with your state university. They may have a local Master Gardener or garden advisor program, and can also probably point you to a local garden club. The web is a fabulous source of information, but you also want people on the ground that know your local conditions and resources. Your local library also probably has a selection of books for local gardeners.

Prepare to enjoy yourself. Put a chair in the garden, and a table for a drink and sit out there with a book. Watch the bugs and birds interact with the plants. Watch the fruit and veg ripe for the kitchen. Yum.

I love this site: http://www.growbetterveggies.com/
the woman who runs it is super nice and helpful, too. Are you taking over for a specific season? Few gardens here in the states will have tomatoes and eggplants in anything but the summer months, the plants flat out die when it gets cold at the end of the season. Citrus usually aren't too demanding, and figs from an established tree just want to be picked for the most part.

Thanks you guys for all the amazing suggestions. I can't wait to get started! To clarify - taking care of the garden is permanent. I'm going to be moving into this place with my fiance, and some of the garden was planted by my fiance's grandfather when his family first moved to America. So it's really important to us that we keep the garden up and in good shape. Frankly, with all the food that's already growing there, I don't think we ever need to hit up a farmer's market or grocery store for produce again.