Back in the early 90s, Disney jumped on the timeshare fervor with Old Key West. They don't call it a timeshare, though. It is a vacation club.
The basic idea is that you purchase x number of points at one of the DVC resorts (currently, Old Key West (OKW), Wilderness Lodge Villas, Beach Club Villas, Boardwalk Villas (all at WDW) as well as Hilton Head and Vero Beach) with a specific anniversary date (they call it a use year) on which you receive your new allotment of points. With the points you purchase, you can make reservations for a studio, 1-BR, 2-BR or 3-BR grand villa. The number of points necessary depend on (1) which resort you choose, (2) which type of room, (3) which nights and how many nights you need, and (4) what time of year you want it.
In addition to your purchase price, you pay monthly association dues. How much they are depends on how many points you "own." You can purchase points at different DVC resorts and with different use years (depending on the number of points you purchase at each). You can purchase directly from Disney or through resale (which typically tend to be lower in cost). Some of the resorts are sold out, so that the only way you can get a contract is through a resale. Disney somewhat regulates the resale market in that they have the right of first purchase when someone is selling their contract.
If you have any other questions, just let us know. There are a lot of DVCers on these boards!