Your wife sounds smart, so with an hour's worth of instruction and four hours with of experimentation she'll have all the basics down. Sit her down in front of a PC, walk her through starting it up and launching a few programs, navigating the start menu, opening and closing directories, what an email program looks like, etc. Do everything you show her the most intuitive way possible. Some of us close programs with alt+F4, some double click the icon in the top left, some right click and close from the task bar, but none of those make anywhere near as much sense as clicking the red X in the top right. When you maximize something, click the boxes in the top right instead of double clicking the bar itself. Don't use the home and end keys when you highlight something, use the mouse. Copy and paste from the edit menu or by right clicking, instead of ctrl+c/v.
The point is to teach her how to figure things out herself, not to teach her a lifetime worth of shortcuts in 48 hours. Ingrain in her that you can't break a computer--ok, it's not really that true, but don't let her be afraid of trying something just because she doesn't know what it will do. Teach her Edit-Undo. If she asks a question you don't know the answer to, load up google and wikipedia so she'll have some places to find answers when you're not around.
Teach her a bit about filesystems--what the C drive is, what the Windows directory is, where should she be saving her files so she can find them later, things like that. I'd start in word, have her mess around a bit, and then ask her how she could do various things. (That is, once she's typed something short, have her use the spell check. Ask her how she would save the file, print it, close out of word completely, and then go back to the same file. If she goes manually to the directory and double clicks the document, ask her if there are any other ways that she might be able to do it in the future.)
The worst thing about learning computers is the mental block that computers are hard--it's not the exact same situation, but my younger brother once complimented me on how fast I typed. I told him that if he'd stop looking at the keyboard when he typed, he could to. I asked him to just try the next time he was on AIM to type out as much as possible without looking at the keyboard. Within a week he was touch typing. He just had a mental block that typing without looking down would be something hard to learn, and a bunch of boring memorization.
On the second day, the two of you can figure out Quicken together.
(Although, if she's used to doing books by hand, she may end up liking something like Excel more, but Quicken will be a lot quicker to get started in if she only has a day.)
Oh, and since you've got the chance right at the beginning, teach her how to RTFM and use the Help file
