The highest resolution, in general, is 640x480 and you can get up to 30fps - but this might not be achievable with dialup.
Any of the better Creative, Logitech, Philips etc will prove a good buy, although the D-Link NetEasy 350 offers an equivalent specification, has a proper CCD, yet costs under £27.
I use one (did a swap with my son for my Creative VideoPlus Webcam as the D-Link gave problems, for some reason, with broadband) and it delivers exactly the same performance as the Creative.
Only letdown is a thickish USB cable and a rather gaudy orange top to the webcam's case.
You can get one at click here
If you look this model up on the net, you won't find it under D-Link but Neteasy....:-)