To the OP: you certainly can make a deposit at the time of your tour/discussion w/the
DVC guide, and you can do so via your Disney Visa...but you can also wait til you get home and mail a check if that's your preference...
TO the next poster: DVC is a time share...but you don't buy specific weeks/times...you buy points which you use to reserve a villa (based on availability) whenever you want to go.
Buying direct from Disney is easy, quick and quite pleasant...you can buy at any of the resorts (WLV, AKV, BCV, BWV, SSR, OKW, VB, HH), even if they're "sold out"--but usually there are no incentives (discounts) to buy at a sold-out resort...prices are around $104/point at the sold-out resorts. Right now, Disney is actively selling the Animal Kingdom Villas and there are incentives...$8 discount per point, some one-year-only "developer points" (ie, points you can use this year only (year is from date of purchase) only at SSR with reservations makeable only 7 months or less prior to your desired dates...
Disney has a minimum buy-in number for your first contract (add-on's allow you to buy far fewer points at a time)...I believe there's a special that lasts til sometime in Sept that will allow you to buy "only" 100 points--the usual minimum for the first contract is 160 points...
That means the minimum buy in price is around $10,000 (too early in the morning for me to do the math!), at AKV for 100 points.
Disney takes credit cards (if you happen to want to do one of those 0 percent interest offers, or for any other reason); they also offer financing...I didn't finance so really don't know much about the financing terms.
Then, there are annual maintenance fees...just shy of $5/point for most of the resorts (each resort's maintenance fees are different)...you pay those every year. You pay for your points only once, when you buy in...and then you get whatever number of points you buy renewed each year (e.g., if you buy 100 points tomorrow, you'll get 100 points this year, and another 100 points each year thereafter until the end of the contract (each resort contract started at 50 years...so each has something less than 50 years left now--the oldest, OKW, has about 32 years or so left on it)...
That's DVC 101 (from the money point of view--there's lots more from the how to use it point of view)...hope the info helps...and obviously, it's possible I remembered something incorrectly...your guide (the DVC rep you discuss this with) will have the info you can rely on! But I'm pretty sure of my facts here...