it sounds like you might not have file sharing turned on. On the 98 machine, go to control panel networking and check your properties for Microsoft Networking. On Win2k pro, go to control panel and Network and Dial-up Connections. Right click on Local Area Connection to verify those proporties as well.
I'm pretty sure File Sharing is not on by default for either one. I'd also advise checking the Linksys website for any warnings about how best to protect File Sharing machines from exposure to evil creepy crawly things out on the internet.