In order to access a shared folder on a Windows 98 machine from an NT-based machine (at least in my experience), you have to have the username that you're logged in with on your XP machine on the 98 machine as well. The easiest way to transfer the plugins would probably be to try to create a share on your XP machine with full write permission. Then, add whatever his log in name on his 98 machine is to your XP machine. Add that name to the list of people with permission to access the shared folder and have him drop the plugins into it. Then, once that's done, disable the share and remove his username from your computer.

AJ