Have a look at this:
http://support.microsoft.com/kb/230205 Try searching for: windows 98 "out of environment space"
with Google.
By the way, Windows 98 is a very old and insecure operating system. I don't know if it's even still officially a supported platform for
Java. If you can, you should try getting a new computer with a newer operating system - Linux, Windows XP or Vista, or Mac OS X. Linux will most likely even run on your old computer and is much more secure than any version of Windows.
[ April 02, 2008: Message edited by: Jesper Young ]