Thunderbird wont match data folder on dual boot

I have Win98 as my main boot and Win2000 as my secondary OS installed
(dual boot). I'm finding myself having to use Win2000 more often lately
because certain things, especially browsers, will no longer work in
Win98. I'm trying to avoid having to install XP, and Win2000 seems to
work fairly well for most of the XP apps. However there is one problem
I cant seem to fix.

I have Thunderbird for email, version 2.x. It's setup and has been used
for years in Win98. When I install it in Win2000, it creates it's own
data folders, rather than using the same folder that has all my emails,
address book, etc in the Win98 installation. This is becoming a hassle,
because I dont want to have to get my email twice, depending on which OS
I'm using. And the way it works now, if I boot to Win2000, to browse
the web, I have to reboot to Win98 to read my email. PAIN IN THE ASS!

Because of this, I'm pretty much stuck using 98, cuz I'm not gonna keep
rebooting all the time. Yet W2000 does a better job of web browsing
since I can use newer browsers.

There must be some way to get Thunderbird to use the same data folder,
but I sure cant figure out how. There must be some setting for this,
but I cant find it. I thought that it would be a simple .ini file to
modify, but no such luck. I dont know if it's in the registry, or where
it is.....

Anyone know how to do this?

Thanks