The computer with Vista will not read a disk prepared on the computer with Windows 98 and e-mailing the pictures is far to slow.

use a cross over cable. It is a special Cat5 Cable with 4 of the 8 wires crossed. You can buy one or have one made for a couple dollars, I think about 25 cents to 33 cents per foot plus $1 per end (you need 2) or a regular cable attached to a network hub. Just share a folder on both computers, drag the pics and save them to a new folder using vista. Or just burn the pics to cd, then load them to the vista machine. (assumming the 98 machine has a cd burner, it likely doesn't)
if you already have both computers online, sharing an internet connection, it is even easier, just make sure file and print sharing is enabled.
OR..
get a free xdrive account, upload from the 98 machine to your online storage, and download to the vista machine.
any of these will work, depending on your set up