Well you hit the nail right on the head. fat32 has a filesize limit of 4gb and theres no way around it i know of. Heres my suggestion, I would copy the 4.5gb file onto the XP laptop, Then on the 98 machine download an ISO of Knoppix Linux (
http://www.knoppix.net/get.php). Knoppix is a Linux distro that comes as a LiveCD which you just boot off of and have a fully wokring linux OS. Burn the knoppix iso and boot off of that. Once your in knoppix there should be a cd/dvd writing program in one of the menus called k3b. From there you should be able to access the file from the WinXp laptop and burn it. Good luck!