My grandmother is 88, and has been using email and browsing the web for four years. All of her siblings (ranging in age from 81 to 90) are connected as well, and now that they're all used to it, I doubt any of them could live without an Internet connection. I actually just put together a slick new system for my grandmother a few months ago (the old one was too slow 😀) and she's been wowing her friends in the retirement home with it.
It's definitely possible to get the elderly hooked on the 'net, but I think it depends on the person.
I would definitely recommend against WebTV, unless your mother still has excellent eyesight, or a huge TV. The television display is not as bright or crisp as a monitor, the text and pictures look like garbage, and it's stuck with the crappy TV resolution. My grandmother found the Internet to be far more enjoyable after my aunts and uncles bought her a new 17" monitor for Christmas two years ago (and now I'm actually wishing I'd pushed them to get a 19" or larger; her eyesight limits her to running only 800 x 600 which is still too low for many of the websites she frequents).
I'd suggest starting her off with whatever you can throw together, with a nice, large monitor. Set everything up to be as easy as possible, and delete all of the icons off of the desktop but My Computer, the Recycle Bin, My Documents, and the internet shortcuts. Make sure there is a shortcut for the dialup connection, and teach her to use that to connect and disconnect (it's far easier than trying to explain how to right click on the little computers down by the clock). Change the mouse settings so that she can easily double-click; trust me, you'll regret it if you don't 😉
Start slow, and teach her one thing at a time. With my grandmother, we started with email. I walked her through the basics of Outlook Express; sending and receiving messages first, and then forwarding and replying to other messages. Once she got the hang of it a little, my mother taught her how to use the address book and how to move messages into different folders. Make sure the preview pane is turned on (sure it's a slight security risk, but it's much easier to clean up a virus than it is to teach an old person how to open individual emails) and make sure OE opens to the Inbox.
Once my grandmother was comfortable with email, we taught her the basics of browsing the Internet (entering addresses, clicking on links, and later how to use a search engine). From there she's learned a lot of it on her own, and now helps the other people in her retirement community if they have questions.
If possible, teach her how to take a screenshot once she starts getting the hang of things. My grandmother now just emails me a picture of the "strange things the computer does" instead of trying to explain it in an email or over the phone. It's saved me time and probably a great many headaches 😉