If you only have one legal IP address, you will not be able to access the win98 machine directly.
However, it is possible to create a PPTP tunnel from the other machine on the internet to the win2k machine. allow the PPTP tunnel to assign an IP address in the same range as the 98 machine and they should rock.
DANGER! that last suggestion is a security risk. PPTP is clear text and the password (so I am told) is only 40 bits.
Another possibility is to pick up a second legal address and a hub/switch and bag ICS.
This comes out of a conversation with my co-worker Mike.
HTH